Add comment about why ansible_ssh_pipelining is set to false in bootstrap-os

cluster.yml

@@ -3,6 +3,8 @@
   any_errors_fatal: true
   gather_facts: false
   vars:
+    # Need to disable pipelining for bootstrap-os as some systems have requiretty in sudoers set, which makes pipelining
+    # fail. bootstrap-os fixes this on these systems, so in later plays it can be enabled.
     ansible_ssh_pipelining: false
   roles:
     - bootstrap-os