Add info about if Snap slow

.github/ISSUE_TEMPLATE.md

@@ -5,6 +5,8 @@ Please report these issues elsewhere:
 - SECURITY ISSUES, PGP EMAIL: https://github.com/wekan/wekan/blob/main/SECURITY.md
 - UCS: https://github.com/wekan/univention/issues
 
+If WeKan Snap is slow, try this: https://github.com/wekan/wekan/wiki/Cron
+
 **[PLEASE UPGRADE](https://github.com/wekan/wekan/wiki/Backup)** to the newest
 WeKan ® before reporting an issue, if possible.