Update ISSUE_TEMPLATE.md

.github/ISSUE_TEMPLATE.md

+# I am taking time off from maintaining this repo. I will not be reviewing issues.
+# Details in https://code.openark.org/blog/mysql/reducing-my-oss-involvement-and-how-it-affects-orchestrator-gh-ost
+
 <!--
  This is the place to report a bug, ask a question, or suggest an enhancement.