languages: Recognize .clangd as YAML (#43557)

Follow-up to: https://github.com/zed-industries/zed/pull/43469

Thanks @WeetHet for [the idea]([WeetHet](https://github.com/WeetHet)).

Release Notes:

- Added support for identifying. .clangd files as YAML by default

docs/src/languages/c.md

@@ -11,6 +11,7 @@ C support is available natively in Zed.
 Clangd out of the box assumes mixed C++/C projects. If you have a C-only project you may wish to instruct clangd to treat all files as C using the `-xc` flag. To do this, create a `.clangd` file in the root of your project with the following:
 
 ```yaml
+# yaml-language-server: $schema=https://json.schemastore.org/clangd.json
 CompileFlags:
   Add: [-xc]
 ```