Add started_talking log message in ReplyOnPause and in api.md (#260)

backend/fastrtc/reply_on_pause.py

@@ -209,6 +209,7 @@ class ReplyOnPause(StreamHandler):
             ):
                 state.started_talking = True
                 logger.debug("Started talking")
+                self.send_message_sync(create_message("log", "started_talking"))
             if state.started_talking:
                 if state.stream is None:
                     state.stream = audio

docs/userguide/api.md

@@ -55,7 +55,7 @@ The `ReplyOnPause` handler can also send the following `log` messages.
 ```json
 {
     "type": "log",
-    "data": "pause_detected" | "response_starting"
+    "data": "pause_detected" | "response_starting" | "started_talking"
 }
 ```