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/servers/mail/postfix/pfixtools.nix

@@ -41,7 +41,7 @@ stdenv.mkDerivation {
   makeFlags = "DESTDIR=$(out) prefix=";
 
   meta = {
-    description = "a collection of postfix-related tools";
+    description = "A collection of postfix-related tools";
     license = with lib.licenses; [ bsd3 ];
     homepage = https://github.com/Fruneau/pfixtools;
   };