update wording of include_context dependency on context capability

Author: ochafik

src/mcp/server/session.py

@@ -240,7 +240,8 @@ async def create_message(
             max_tokens: Maximum number of tokens to generate.
             system_prompt: Optional system prompt.
             include_context: Optional context inclusion setting.
-                Requires client to have sampling.context capability.
+                Should only be set to "thisServer" or "allServers"
+                if the client has sampling.context capability.
             temperature: Optional sampling temperature.
             stop_sequences: Optional stop sequences.
             metadata: Optional metadata to pass through to the LLM provider.