Improve error handling

[jvandemo]

Feedback from @sindresorhus:

I think these FAQs should rather be actually improved errors instead of documenting bad errors

Link: https://twitter.com/sindresorhus/status/655822910758588416

[jvandemo]

When an error is encountered during a call to the GitHub API, the API returns just a simple string like:

• Bad Credentials
• Validation Failed
• etc...

without any context of the label.

The CLI relays this information but the quality of the feedback is too poor to provide consumers with enough insights to clearly see what's happening:

Ideally we should be able to display:

• which label failed
• what error occurred

to improve developer experience.