fix url for webhook

tsa/howto/gitlab.md

@@ -77,12 +77,13 @@ By default, new projects do *not* have notifications setup in
 "Webhook", in the `Settings -> Webhooks` section of the project. The
 URL should be:
 
-    https://kgb-bot.torproject.org/webhook/?channel=%23tor-bots
+    https://kgb-bot.torproject.org/webhook/
 
 ... and you should select the notifications you wish to see in
 `#tor-bots`. You can also enable notifications to other channels by
-adding more parameters to the URL. The parameters are documented the
-[KGB documentation](https://salsa.debian.org/kgb-team/kgb/-/wikis/usage).
+adding more parameters to the URL, like (say)
+`?channel=%23tor-foo`. The parameters are documented the [KGB
+documentation](https://salsa.debian.org/kgb-team/kgb/-/wikis/usage).
 
 Note that GitLab admins might be able to configure [system-wide
 hooks](https://gitlab.torproject.org/help/system_hooks/system_hooks) in [the admin section](https://gitlab.torproject.org/admin/hooks), although it's not entirely clear