Update documentation

[anulman]

Per @ibrahimab's note on #324, e-electron docs are useful but do not do a great job indicating where to look upstream for valid config options / debug support.

We should take a look at documentation and make sure at least the following are covered:

README.md

• Quickstart
• What is electron-forge?
• Basic info re devtron

Docs dir (+ site?)

• Per-command documentation
• Common configuration options / settings
• Detailed debugging instructions
• File structure
• ASAR handling (per Documentation not clear about unpackDir - How to use it? #242)

Misc

• Consider CONTRIBUTING.md + issues template?

[jacobq]

Ref #404

@rwwagner90 If you have other ideas about how to improve the docs perhaps this would be a good place to discuss. Sadly things have gotten pretty stale :/

[bendemboski]

Documentation refreshed in v3. If there are still issues, please open new issues.