Re-add ftplugin for markdown files

modules2/nixvim/ftplugin/markdown.nix

@@ -0,0 +1,22 @@
+{
+  flake.modules.nixvim.custom = {
+    plugins.cmp-path.enable = true;
+
+    extraFiles."after/ftplugin/markdown.lua".text =
+      # lua
+      ''
+        local opt = vim.opt_local
+
+        opt.spell = true
+        opt.wrap = true
+
+        local cmp = require "cmp"
+        local sources = cmp.get_config().sources
+
+        -- TODO: confirm these aren't aleady in the list of sources to avoid duplicate suggestions.
+        table.insert(sources, { name = "path" })
+
+        cmp.setup.buffer { sources = sources }
+      '';
+  };
+}