feat(plugins): Add [iamcco/markdown-preview.nvim](https://github.com/iamcco/markdown-preview.nvim/)

nix/neovim-overlay.nix

@@ -81,6 +81,7 @@ with final.pkgs.lib; let
     # ^ UI
 
     # language support
+    markdown-preview-nvim
     # ^ language support
 
     # navigation/editing enhancement plugins

nvim/plugin/keymaps.lua

@@ -60,6 +60,8 @@ require('which-key').add({
     end,
     desc = "trouble: load [w]orkspace"
   },
+
+  { "<leader>lP", "<cmd>MarkdownPreviewToggle<cr>",                             desc = "Markdown [l] [P]review"},
 })
 
 -- Toggle the quickfix list (only opens if it is populated)