nvim: Add markdown-toc plugin

nvim/.config/nvim/lua/plugins/markdown_toc.lua

@@ -0,0 +1,7 @@
+return {
+    "hedyhli/markdown-toc.nvim",
+    cmd = {
+        "Mtoc"
+    }, -- Or, lazy load on "Mtoc" command
+    opts = {}
+}