Captialize meta.description of all packages

In line with the Nixpkgs manual.

A mechanical change, done with this command:

  find pkgs -name "*.nix" | \
      while read f; do \
          sed -e 's/description\s*=\s*"\([a-z]\)/description = "\u\1/' -i "$f"; \
      done

I manually skipped some:

* Descriptions starting with an abbreviation, a user name or package name
* Frequently generated expressions (haskell-packages.nix)

pkgs/development/tools/misc/distcc/default.nix

@@ -70,7 +70,7 @@ let
     };
 
     meta = {
-      description = "a fast, free distributed C/C++ compiler";
+      description = "A fast, free distributed C/C++ compiler";
       homepage = "http://distcc.org";
       license = "GPL";