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/command-not-found/command-not-found.nix

@@ -31,13 +31,14 @@ let
 
 in {
   options.programs.command-not-found = {
-    enable = mkEnableOption "command-not-found hook for interactive shell";
+    enable =
+      mkEnableOption (lib.mdDoc "command-not-found hook for interactive shell");
 
     dbPath = mkOption {
       default =
         "/nix/var/nix/profiles/per-user/root/channels/nixos/programs.sqlite";
-      description = ''
-        Absolute path to <filename>programs.sqlite</filename>. By
+      description = lib.mdDoc ''
+        Absolute path to {file}`programs.sqlite`. By
         default this file will be provided by your channel
         (nixexprs.tar.xz).
       '';