docs: add dispatcher trouble-shooting notes
documenting
teuthology-dispatcher
-===============
+=====================
.. program-output:: teuthology-dispatcher --help
+
+trouble-shooting notes:
+=======================
+
+- Github unreachable kills dispatcher - The dispatcher might be killed when github becomes unreachable, e.g., https://tracker.ceph.com/issues/54366
\ No newline at end of file
