add debugging info to debugging page as well

.github/CONTRIBUTING.md

@@ -293,7 +293,7 @@ Acceptance tests typically require other environment variables to be set for
 things such as API tokens and keys. Each test should error and tell you which
 credentials are missing, so those are not documented here.
 
-#### Debugging
+#### Debugging Plugins
 
 Each packer plugin runs in a separate process and communicates with RCP over a
 socket therefore using a debugger will not work (be complicated at least).

website/source/docs/other/debugging.html.md

@@ -71,6 +71,15 @@ to force the log to always go to a specific file when logging is enabled. Note
 that even when `PACKER_LOG_PATH` is set, `PACKER_LOG` must be set in order for
 any logging to be enabled.
 
+### Debugging Plugins
+
+Each packer plugin runs in a separate process and communicates with RCP over a
+socket therefore using a debugger will not work (be complicated at least).
+
+But most of the Packer code is really simple and easy to follow with PACKER_LOG
+turned on. If that doesn't work adding some extra debug print outs when you have
+homed in on the problem is usually enough.
+
 ### Debugging Packer in Powershell/Windows
 
 In Windows you can set the detailed logs environmental variable `PACKER_LOG` or