treewide: convert all option docs to Markdown

This process was automated by [my fork of `nix-doc-munge`]. All
conversions were automatically checked to produce the same DocBook
result when converted back, modulo minor typographical/formatting
differences on the acceptable-to-desirable spectrum.

To reproduce this commit, run:

  $ NIX_PATH=nixpkgs=flake:nixpkgs/e7e69199f0372364a6106a1e735f68604f4c5a25 \
    nix shell nixpkgs#coreutils \
    -c find . -name '*.nix' \
    -exec nix run -- github:emilazy/nix-doc-munge/98dadf1f77351c2ba5dcb709a2a171d655f15099 \
    {} +
  $ ./format

[my fork of `nix-doc-munge`]: https://github.com/emilazy/nix-doc-munge/tree/home-manager

modules/i18n/input-method/default.nix

@@ -65,7 +65,7 @@ in {
         internal = true;
         type = types.nullOr types.path;
         default = null;
-        description = ''
+        description = lib.mdDoc ''
           The input method method package.
         '';
       };

modules/i18n/input-method/fcitx5.nix

@@ -13,7 +13,7 @@ in {
         type = with types; listOf package;
         default = [ ];
         example = literalExpression "with pkgs; [ fcitx5-rime ]";
-        description = ''
+        description = lib.mdDoc ''
           Enabled Fcitx5 addons.
         '';
       };

modules/i18n/input-method/kime.nix

@@ -26,9 +26,9 @@ in {
             };
           }
         '';
-        description = ''
+        description = lib.mdDoc ''
           kime configuration. Refer to
-          <link xlink:href="https://github.com/Riey/kime/blob/develop/docs/CONFIGURATION.md"/>
+          <https://github.com/Riey/kime/blob/develop/docs/CONFIGURATION.md>
           for details on supported values.
         '';
       };

modules/i18n/input-method/uim.nix

@@ -11,7 +11,7 @@ in {
         type = types.enum [ "gtk" "gtk3" "gtk-systray" "gtk3-systray" "qt4" ];
         default = "gtk";
         example = "gtk-systray";
-        description = ''
+        description = lib.mdDoc ''
           Selected UIM toolbar.
         '';
       };