Refine the prompt for add_docs command

I found that without it, python docstrings are sometimes suggested above the function signature, instead of below.

pr_agent/settings/pr_add_docs.toml

@@ -69,6 +69,7 @@ Code Documentation:
         - after
       description: |-
         The {{ docs_for_language }} placement relative to the relevant line (code component).
+        For example, in Python the docs are placed after the function signature, but in Java they are placed before.
     documentation:
       type: string
       description: |-