treewide: automatically md-convert option descriptions

the conversion procedure is simple:

 - find all things that look like options, ie calls to either `mkOption`
   or `lib.mkOption` that take an attrset. remember the attrset as the
   option
 - for all options, find a `description` attribute who's value is not a
   call to `mdDoc` or `lib.mdDoc`
 - textually convert the entire value of the attribute to MD with a few
   simple regexes (the set from mdize-module.sh)
 - if the change produced a change in the manual output, discard
 - if the change kept the manual unchanged, add some text to the
   description to make sure we've actually found an option. if the
   manual changes this time, keep the converted description

this procedure converts 80% of nixos options to markdown. around 2000
options remain to be inspected, but most of those fail the "does not
change the manual output check": currently the MD conversion process
does not faithfully convert docbook tags like <code> and <package>, so
any option using such tags will not be converted at all.

nixos/modules/virtualisation/docker.nix

@@ -21,11 +21,11 @@ in
         type = types.bool;
         default = false;
         description =
-          ''
+          lib.mdDoc ''
             This option enables docker, a daemon that manages
             linux containers. Users in the "docker" group can interact with
             the daemon (e.g. to start or stop containers) using the
-            <command>docker</command> command line tool.
+            {command}`docker` command line tool.
           '';
       };
 
@@ -34,7 +34,7 @@ in
         type = types.listOf types.str;
         default = ["/run/docker.sock"];
         description =
-          ''
+          lib.mdDoc ''
             A list of unix and tcp docker should listen to. The format follows
             ListenStream as described in systemd.socket(5).
           '';
@@ -45,10 +45,10 @@ in
         type = types.bool;
         default = true;
         description =
-          ''
+          lib.mdDoc ''
             When enabled dockerd is started on boot. This is required for
             containers which are created with the
-            <literal>--restart=always</literal> flag to work. If this option is
+            `--restart=always` flag to work. If this option is
             disabled, docker might be started on demand by socket activation.
           '';
       };
@@ -61,7 +61,7 @@ in
           ipv6 = true;
           "fixed-cidr-v6" = "fd00::/80";
         };
-        description = ''
+        description = lib.mdDoc ''
           Configuration for docker daemon. The attributes are serialized to JSON used as daemon.conf.
           See https://docs.docker.com/engine/reference/commandline/dockerd/#daemon-configuration-file
         '';
@@ -71,7 +71,7 @@ in
       mkOption {
         type = types.bool;
         default = false;
-        description = ''
+        description = lib.mdDoc ''
           Enable nvidia-docker wrapper, supporting NVIDIA GPUs inside docker containers.
         '';
       };
@@ -81,7 +81,7 @@ in
         type = types.bool;
         default = true;
         description =
-          ''
+          lib.mdDoc ''
             Allow dockerd to be restarted without affecting running container.
             This option is incompatible with docker swarm.
           '';
@@ -92,7 +92,7 @@ in
         type = types.nullOr (types.enum ["aufs" "btrfs" "devicemapper" "overlay" "overlay2" "zfs"]);
         default = null;
         description =
-          ''
+          lib.mdDoc ''
             This option determines which Docker storage driver to use. By default
             it let's docker automatically choose preferred storage driver.
           '';
@@ -103,7 +103,7 @@ in
         type = types.enum ["none" "json-file" "syslog" "journald" "gelf" "fluentd" "awslogs" "splunk" "etwlogs" "gcplogs"];
         default = "journald";
         description =
-          ''
+          lib.mdDoc ''
             This option determines which Docker log driver to use.
           '';
       };
@@ -113,9 +113,9 @@ in
         type = types.separatedString " ";
         default = "";
         description =
-          ''
+          lib.mdDoc ''
             The extra command-line options to pass to
-            <command>docker</command> daemon.
+            {command}`docker` daemon.
           '';
       };
 
@@ -123,10 +123,10 @@ in
       enable = mkOption {
         type = types.bool;
         default = false;
-        description = ''
+        description = lib.mdDoc ''
           Whether to periodically prune Docker resources. If enabled, a
-          systemd timer will run <literal>docker system prune -f</literal>
-          as specified by the <literal>dates</literal> option.
+          systemd timer will run `docker system prune -f`
+          as specified by the `dates` option.
         '';
       };
 
@@ -134,8 +134,8 @@ in
         type = types.listOf types.str;
         default = [];
         example = [ "--all" ];
-        description = ''
-          Any additional flags passed to <command>docker system prune</command>.
+        description = lib.mdDoc ''
+          Any additional flags passed to {command}`docker system prune`.
         '';
       };
 
@@ -155,7 +155,7 @@ in
       default = pkgs.docker;
       defaultText = literalExpression "pkgs.docker";
       type = types.package;
-      description = ''
+      description = lib.mdDoc ''
         Docker package to be used in the module.
       '';
     };