[Docs]: Update README and Contributing guidelines

[fokusferit]

Updated list of things I will cover:

• Migrate documentation
• CLI descriptions at webpack.js.org and in the CLI should be more descriptive
• README in all the package folders for each package
• InIt documentation at webpack.js.org
• Documentation and Contribution guide
• Explaination about publishing and the next/develop branch
• Explain empty params code style

[evenstensberg]

For the contribution guides, it should be split into sections like: do you want to make an easy contribution or an advanced one. At the start, we could have a small summary, and maybe split it up into a menu with pointers to different guides. One could be tests, another AST et.al

[dhruvdutt]

@ev1stensberg Can we add "help wanted", "Good First Contribution" tags?

[evenstensberg]

This is an maintainer issue, cause we need to make sure that the structure and documentation reflects how we want people to contribute. Discussed this in a meeting, @fokusferit can give you the link

[evenstensberg]

@fokusferit any update? 💯

[evenstensberg]

Moving #450 here

[evenstensberg]

So here's what needs attention:

1. Migrate documentation

2. InIt documentation at webpack.js.org

3. CLI descriptions at webpack.js.org and in the CLI should be more descriptive

4. README in all the package folders for each package

5. Documentation and Contribution guide

6. Explaination about publishing and the next/develop branch

[fokusferit]

I'm updating the initial comment, and create a checklist, so that I it's easier to reference to PR's for each task.