chore: update serena project config

Author: marconae

.serena/project.yml

@@ -126,3 +126,10 @@ initial_prompt: ""
 # override of the corresponding setting in serena_config.yml, see the documentation there.
 # If null or missing, the value from the global config is used.
 symbol_info_budget:
+
+# The language backend to use for this project.
+# If not set, the global setting from serena_config.yml is used.
+# Valid values: LSP, JetBrains
+# Note: the backend is fixed at startup. If a project with a different backend
+# is activated post-init, an error will be returned.
+language_backend: