Add buildpack debugging documentation

Previously there was no documentation around debugging the buildpack.
This lead to having to provide that information on mailing lists and
in issues.  This change adds documentation about debug logging and
running the buildpack locally.

[#69986486][resolves #50]
Merge 69986486-buildpack-debug to master

[Completes #69986486]
Merge remote-tracking branch 'upstream/master'