Add warning about deadlocks if calling call_async_task from eventloop

Author: julianstirling

src/labthings_fastapi/thing_server_interface.py

@@ -116,6 +116,8 @@ def call_async_task(
         block the current thread while it calls the provided async function in the
         server's event loop.
 
+        Do not call this from the event loop or it may lead to a deadlock.
+
         :param async_function: the asynchronous function to call.
         :param \*args: positional arguments to be provided to the function.