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/tools/backup/rdiff-backup/default.nix

@@ -21,7 +21,7 @@ stdenv.mkDerivation {
   buildInputs = [ python librsync gnused ];
 
   meta = {
-    description = "backup system trying to combine best a mirror and an incremental backup system";
+    description = "Backup system trying to combine best a mirror and an incremental backup system";
     homepage = http://rdiff-backup.nongnu.org/;
     license = stdenv.lib.licenses.gpl2;
     platforms = stdenv.lib.platforms.all;