Warn about admin privilege to disable GitHub Webhooks

[ci skip]

app/views/import/github/status.html.haml

@@ -6,7 +6,7 @@
 
 %p
   %i.fa.fa-warning
-  To import GitHub pull requests, any pull request source branches that had been deleted are temporarily restored on GitHub. To prevent any connected CI services from being overloaded with dozens of irrelevant branches being created and deleted again, GitHub webhooks are temporarily disabled during the import process.
+  To import GitHub pull requests, any pull request source branches that had been deleted are temporarily restored on GitHub. To prevent any connected CI services from being overloaded with dozens of irrelevant branches being created and deleted again, GitHub webhooks are temporarily disabled during the import process, but only if you have admin access to the GitHub repository.
 
 %p.light
   Select projects you want to import.