docs: Write a beginner doc on traceback.

[trueskawka]

While discussing the bash doc for newbies, I've had an idea on a traceback doc, that should:

• inform what a traceback is
• explain how to use it to use it to understand issues, with some help from googling the relevant errors
• explain how to share it in a meaningful way

Sharing and discussing problems is a skill to be learned and traceback can be confusing.