Update pull-from-upstream retriggering documentation (#722)

Update pull-from-upstream retriggering documentation

Reviewed-by: Maja Massarini
Reviewed-by: Laura Barcziová
Reviewed-by: František Lachman <flachman@redhat.com>

docs/fedora-releases-guide.md

@@ -144,6 +144,10 @@ via a comment in any dist-git pull request:
 
     /packit pull-from-upstream
 
+This will take the Packit configuration file from the `rawhide` dist-git branch, same as if the job was triggered by a new release. To use the configuration file from the dist-git pull request you are commenting on, you can add an argument:
+
+    /packit pull-from-upstream --with-pr-config
+
 ## Koji build job
 After having the dist-git content updated, you can easily automate also building in Koji.
 You can simply configure Packit to react to the new commits in your dist-git repository and create