Revert "nixos/doc: re-format"

This reverts commit ea6e8775bd. The new
format is not an improvement.

nixos/doc/manual/development/sources.xml

@@ -5,47 +5,77 @@
         xml:id="sec-getting-sources">
  <title>Getting the Sources</title>
  <para>
-  By default, NixOS’s <command>nixos-rebuild</command> command uses the NixOS and Nixpkgs sources provided by the <literal>nixos</literal> channel (kept in <filename>/nix/var/nix/profiles/per-user/root/channels/nixos</filename>). To modify NixOS, however, you should check out the latest sources from Git. This is as follows:
+  By default, NixOS’s <command>nixos-rebuild</command> command uses the NixOS
+  and Nixpkgs sources provided by the <literal>nixos</literal> channel (kept in
+  <filename>/nix/var/nix/profiles/per-user/root/channels/nixos</filename>). To
+  modify NixOS, however, you should check out the latest sources from Git. This
+  is as follows:
 <screen>
 <prompt>$ </prompt>git clone https://github.com/NixOS/nixpkgs
 <prompt>$ </prompt>cd nixpkgs
 <prompt>$ </prompt>git remote add channels https://github.com/NixOS/nixpkgs-channels
 <prompt>$ </prompt>git remote update channels
 </screen>
-  This will check out the latest Nixpkgs sources to <filename>./nixpkgs</filename> the NixOS sources to <filename>./nixpkgs/nixos</filename>. (The NixOS source tree lives in a subdirectory of the Nixpkgs repository.) The remote <literal>channels</literal> refers to a read-only repository that tracks the Nixpkgs/NixOS channels (see <xref linkend="sec-upgrading"/> for more information about channels). Thus, the Git branch <literal>channels/nixos-17.03</literal> will contain the latest built and tested version available in the <literal>nixos-17.03</literal> channel.
+  This will check out the latest Nixpkgs sources to
+  <filename>./nixpkgs</filename> the NixOS sources to
+  <filename>./nixpkgs/nixos</filename>. (The NixOS source tree lives in a
+  subdirectory of the Nixpkgs repository.) The remote
+  <literal>channels</literal> refers to a read-only repository that tracks the
+  Nixpkgs/NixOS channels (see <xref linkend="sec-upgrading"/> for more
+  information about channels). Thus, the Git branch
+  <literal>channels/nixos-17.03</literal> will contain the latest built and
+  tested version available in the <literal>nixos-17.03</literal> channel.
  </para>
  <para>
-  It’s often inconvenient to develop directly on the master branch, since if somebody has just committed (say) a change to GCC, then the binary cache may not have caught up yet and you’ll have to rebuild everything from source. So you may want to create a local branch based on your current NixOS version:
+  It’s often inconvenient to develop directly on the master branch, since if
+  somebody has just committed (say) a change to GCC, then the binary cache may
+  not have caught up yet and you’ll have to rebuild everything from source.
+  So you may want to create a local branch based on your current NixOS version:
 <screen>
 <prompt>$ </prompt>nixos-version
 17.09pre104379.6e0b727 (Hummingbird)
 
 <prompt>$ </prompt>git checkout -b local 6e0b727
 </screen>
-  Or, to base your local branch on the latest version available in a NixOS channel:
+  Or, to base your local branch on the latest version available in a NixOS
+  channel:
 <screen>
 <prompt>$ </prompt>git remote update channels
 <prompt>$ </prompt>git checkout -b local channels/nixos-17.03
 </screen>
-  (Replace <literal>nixos-17.03</literal> with the name of the channel you want to use.) You can use <command>git merge</command> or <command>git rebase</command> to keep your local branch in sync with the channel, e.g.
+  (Replace <literal>nixos-17.03</literal> with the name of the channel you want
+  to use.) You can use <command>git merge</command> or <command>git
+  rebase</command> to keep your local branch in sync with the channel, e.g.
 <screen>
 <prompt>$ </prompt>git remote update channels
 <prompt>$ </prompt>git merge channels/nixos-17.03
 </screen>
-  You can use <command>git cherry-pick</command> to copy commits from your local branch to the upstream branch.
+  You can use <command>git cherry-pick</command> to copy commits from your
+  local branch to the upstream branch.
  </para>
  <para>
-  If you want to rebuild your system using your (modified) sources, you need to tell <command>nixos-rebuild</command> about them using the <option>-I</option> flag:
+  If you want to rebuild your system using your (modified) sources, you need to
+  tell <command>nixos-rebuild</command> about them using the
+  <option>-I</option> flag:
 <screen>
 <prompt># </prompt>nixos-rebuild switch -I nixpkgs=<replaceable>/my/sources</replaceable>/nixpkgs
 </screen>
  </para>
  <para>
-  If you want <command>nix-env</command> to use the expressions in <replaceable>/my/sources</replaceable>, use <command>nix-env -f <replaceable>/my/sources</replaceable>/nixpkgs</command>, or change the default by adding a symlink in <filename>~/.nix-defexpr</filename>:
+  If you want <command>nix-env</command> to use the expressions in
+  <replaceable>/my/sources</replaceable>, use <command>nix-env -f
+  <replaceable>/my/sources</replaceable>/nixpkgs</command>, or change the
+  default by adding a symlink in <filename>~/.nix-defexpr</filename>:
 <screen>
 <prompt>$ </prompt>ln -s <replaceable>/my/sources</replaceable>/nixpkgs ~/.nix-defexpr/nixpkgs
 </screen>
-  You may want to delete the symlink <filename>~/.nix-defexpr/channels_root</filename> to prevent root’s NixOS channel from clashing with your own tree (this may break the command-not-found utility though). If you want to go back to the default state, you may just remove the <filename>~/.nix-defexpr</filename> directory completely, log out and log in again and it should have been recreated with a link to the root channels.
+  You may want to delete the symlink
+  <filename>~/.nix-defexpr/channels_root</filename> to prevent root’s NixOS
+  channel from clashing with your own tree (this may break the
+  command-not-found utility though). If you want to go back to the default
+  state, you may just remove the <filename>~/.nix-defexpr</filename> directory
+  completely, log out and log in again and it should have been recreated with a
+  link to the root channels.
  </para>
 <!-- FIXME: not sure what this means.
 <para>You should not pass the base directory