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/programs/bottom.nix

@@ -11,25 +11,25 @@ let
 in {
   options = {
     programs.bottom = {
-      enable = mkEnableOption ''
+      enable = mkEnableOption (lib.mdDoc ''
         bottom, a cross-platform graphical process/system monitor with a
-        customizable interface'';
+        customizable interface'');
 
       package = mkOption {
         type = types.package;
         default = pkgs.bottom;
         defaultText = literalExpression "pkgs.bottom";
-        description = "Package providing <command>bottom</command>.";
+        description = lib.mdDoc "Package providing {command}`bottom`.";
       };
 
       settings = mkOption {
         type = tomlFormat.type;
         default = { };
-        description = ''
+        description = lib.mdDoc ''
           Configuration written to
-          <filename>$XDG_CONFIG_HOME/bottom/bottom.toml</filename>.
-          </para><para>
-          See <link xlink:href="https://github.com/ClementTsang/bottom/blob/master/sample_configs/default_config.toml"/>
+          {file}`$XDG_CONFIG_HOME/bottom/bottom.toml`.
+
+          See <https://github.com/ClementTsang/bottom/blob/master/sample_configs/default_config.toml>
           for the default configuration.
         '';
         example = literalExpression ''