Update tools.mdx

docs/servers/tools.mdx

@@ -205,6 +205,10 @@ FastMCP automatically converts the value returned by your function into the appr
 
 FastMCP will attempt to serialize other types to a string if possible.
 
+<Tip>
+At this time, FastMCP responds only to your tool's return *value*, not its return *annotation*.
+</Tip>
+
 ```python
 from fastmcp import FastMCP, Image
 import io