Add "cause" and references as known to troubleshooting guide

[blsaws]

In netarbiter/sds/ceph-docker/examples/helm/TROUBLESHOOT.md, the issues noted should be further explained in a section "cause" (as known, or "cause TBD") with references as may be helpful for users who might need to apply the workaround/fix for similar (but not exact) errors. Also note whether the workaround/fix has already been applied in the repo, by default.

[knowpd]

TROUBLESHOOTING.md is offered to share the issues that I encountered. It is likely to have many different causes for a similar symptom. Use this document just for reference.

Hee Won Lee knowpd@research.att.com