docs: Proto formatter example (#20677)

docs/src/languages/proto.md

@@ -3,3 +3,41 @@
 Proto/proto3 (Protocol Buffers definition language) support is available natively in Zed.
 
 - Tree Sitter: [coder3101/tree-sitter-proto](https://github.com/coder3101/tree-sitter-proto)
+- Language Server: [protols](https://github.com/coder3101/protols)
+
+## Formatting
+
+ProtoLS supports formatting if you have `clang-format` installed.
+
+```sh
+# MacOS:
+brew install clang-format
+# Ubuntu
+sudo apt-get install clang-format
+# Fedora
+sudo dnf install clang-tools-extra
+```
+
+To customize your formatting preferences, create a `.clang-format` file, e.g.:
+
+```clang-format
+IndentWidth: 4
+ColumnLimit: 120
+```
+
+Or you can have zed directly invoke `clang-format` by specifying it as a [formatter](https://zed.dev/docs/configuring-zed#formatter) in your settings:
+
+```json
+  "languages": {
+    "Proto": {
+      "format_on_save": "on",
+      "tab_size": 4,
+      "formatter": {
+        "external": {
+          "command": "clang-format",
+          "arguments": ["-style={IndentWidth: 4, ColumnLimit: 0}"]
+        }
+      }
+    },
+  }
+```