docs: Update language docs and include links in the sidebar (#13828)

This PR updates the supported language docs and adds them to the sidebar
for better discoverability.

Release Notes:

- N/A

docs/src/languages/html.md

@@ -1,4 +1,15 @@
 # HTML
 
-- Tree Sitter: [tree-sitter-html](https://github.com/tree-sitter/tree-sitter-html)
-- Language Server: [vscode-html-language-server](https://github.com/hrsh7th/vscode-langservers-extracted)
+HTML support is available through the [HTML extension](https://github.com/zed-industries/zed/tree/main/extensions/html).
+
+This extension is automatically installed.
+
+If you do not want to use the HTML extension, you can add the following to your settings:
+
+```json
+{
+  "auto_install_extensions": {
+    "html": false
+  }
+}
+```