Update ISSUE_TEMPLATE

Author: arnaud-lb

.github/ISSUE_TEMPLATE

@@ -2,7 +2,8 @@
 Thank you for creating a ticket!
 
 Before submitting the ticket, please consider asking a question on the
-Gitter channel at https://gitter.im/arnaud-lb/php-rdkafka
+Gitter channel at https://gitter.im/arnaud-lb/php-rdkafka, or
+on the Google Groups at https://groups.google.com/forum/#!forum/php-rdkafka
 
 If you are reporting a bug, please provide the following informations:
 -->