Clarify grammar in FAQ about worker restarts

Noticed by @guettli on GitHub, this sentence was likely supposed to say
that workers may "be killed" and "start up", where "to start up" is a
verb phrase while "startup" is a single word noun. Clarify by changing
this to read "to stop and start".

Author: tilgovi

docs/source/faq.rst

@@ -216,7 +216,7 @@ If you use a reverse proxy like NGINX you might see 502 returned to a client.
 
 In the gunicorn logs you might simply see ``[35] [INFO] Booting worker with pid: 35``
 
-It's completely normal for workers to be killed and startup, for example due to
+It's completely normal for workers to be stop and start, for example due to
 max-requests setting. Ordinarily gunicorn will capture any signals and log something.
 
 This particular failure case is usually due to a SIGKILL being received, as it's