languages/render-markdown-nvim: add file_types as list

set file_types as listOf (nullOr str) to allow merging

docs/release-notes/rl-0.8.md

@@ -344,3 +344,7 @@
 [howird](https://github.com/howird):
 
 - Change python dap adapter name from `python` to commonly expected `debugpy`.
+
+[aionoid](https://github.com/aionoid):
+
+- Fix [render-markdown.nvim] file_types option type to list, to accept merging.

modules/plugins/languages/markdown.nix

@@ -9,7 +9,7 @@
   inherit (lib.modules) mkIf mkMerge;
   inherit (lib.options) mkEnableOption mkOption;
   inherit (lib.lists) isList;
-  inherit (lib.types) bool enum either package listOf str;
+  inherit (lib.types) bool enum either package listOf str nullOr;
   inherit (lib.nvim.lua) expToLua toLuaObject;
   inherit (lib.nvim.types) diagnostics mkGrammarOption mkPluginSetupOption;
   inherit (lib.nvim.dag) entryAnywhere;
@@ -117,7 +117,13 @@ in {
             '';
           };
 
-        setupOpts = mkPluginSetupOption "render-markdown" {};
+        setupOpts = mkPluginSetupOption "render-markdown" {
+          file_types = lib.mkOption {
+            type = listOf (nullOr str);
+            default = [];
+            description = "List of buffer filetypes to enable this plugin in. This will cause the plugin to attach to new buffers who have any of these filetypes.";
+          };
+        };
       };
     };