Add markdown preview plugin

lua/custom/plugins/markdown_preview.lua

@@ -0,0 +1,11 @@
+return {
+  "iamcco/markdown-preview.nvim",
+  cmd = { "MarkdownPreviewToggle", "MarkdownPreview", "MarkdownPreviewStop" },
+  build = "cd app && npm install && git restore .",
+  -- or if you use yarn: (I have not checked this, I use npm)
+  -- build = "cd app && yarn install && git restore .",
+  init = function()
+    vim.g.mkdp_filetypes = { "markdown" }
+  end,
+  ft = { "markdown" },
+}