Add RCCL debugging guide (#1420)

* Add RCCL debugging guide

* Changes from external review

* More edits from internal review

* Additional edits

* Minor correction

* More changes after external review

* Integrate index and ToC changes with incoming merge changes

* Integrate feedback from management review

* Minor edits from the internal review

[ROCm/rccl commit: 6d34fb7632]

projects/rccl/docs/sphinx/_toc.yml.in

@@ -18,6 +18,8 @@ subtrees:
   entries:
   - file: how-to/using-nccl
     title: Using the NCCL Net plugin
+  - file: how-to/troubleshooting-rccl
+    title: Troubleshoot RCCL
   - file: how-to/rccl-usage-tips
 
 - caption: Examples