Add $entry->isSlowQuery() in documentation.

As this PR has been merged I think it's better to add the method in documentation so it will be easier for developers to find it.


laravel/telescope#1146

telescope.md

@@ -183,6 +183,7 @@ You may filter the data that is recorded by Telescope via the `filter` closure t
             return $entry->isReportableException() ||
                 $entry->isFailedJob() ||
                 $entry->isScheduledTask() ||
+                $entry->isSlowQuery() ||
                 $entry->hasMonitoredTag();
         });
     }