Add guideline on how to work on GitHub issues

[zzap]

It seems that we have developed a sort of a workflow for working on thsese issues but no one knows about it. Since we don't have PRs here we can't use some other GitHub features, such as "Request review" etc. Also, due to permissions, contributors can't assign themselves or move issues through our project boards.

So we have workarounds:

• You browse issues and find what you like. Post in comment that you'd like to work on it and start working.
• Someone will assign you and move issue into "In progress" column.
• When your work is ready for review, post another comment mentioning @zzap , @atachibana or someone else if you were discussing it with someone else.
• Someone will move issue to "Review" column. After review you'll be either asked to fix something or if you'd like to update documentation yourself.
• When documentation is updated the issue is moved to "Done" column.

Let's add it to README file here and our Handbook.

[atachibana]

I inserted new page to that Docs Handbook so that it includes your sentences: https://make.wordpress.org/docs/handbook/workflows/fixing-an-issue/

Feel free to edit it.

Also, I modified the Docs Handbook by removing old articles, adding recent information

https://make.wordpress.org/docs/handbook/get-involved/ https://make.wordpress.org/docs/handbook/get-involved/getting-started-at-a-contributor-day/ https://make.wordpress.org/docs/handbook/get-involved/current-docs-projects/ https://make.wordpress.org/docs/handbook/github-repository-and-projects/ https://make.wordpress.org/docs/handbook/workflows/reporting-an-issue/ https://make.wordpress.org/docs/handbook/helphub/ https://make.wordpress.org/docs/handbook/helphub/migrating-articles/

[atachibana]

@zzap This repositories 'Resolving Issues' section in both README.md and CONTRIBUTING.md should be modified as like as Docs Handbook:

Resolving Issues

(Replace current Step 1 - 3 by following steps)

1. You browse issues and find what you like. Post in comment that you'd like to work on it and start working.
2. Someone will assign you and move issue into "In progress" column.
3. When your work is ready for review, post another comment mentioning @zzap , @atachibana or someone else if you were discussing it with someone else.
4. Someone will move issue to "Review" column. After review you'll be either asked to fix something or if you'd like to update documentation yourself.
5. When documentation is updated the issue is moved to "Done" column.