Add YAML to the list of supported programming languages

YAML is already supported based on RedHat's yaml-language-server.

docs/01-about/020_programming-languages.md

@@ -58,6 +58,7 @@ With Serena, we provide direct, out-of-the-box support for:
   (requires some [manual setup](../03-special-guides/scala_setup_guide_for_serena); uses Metals LSP)
 * **Swift**
 * **TypeScript**
+* **YAML**
 * **Zig**  
   (requires installation of ZLS - Zig Language Server)