Add a "Contribute" tab to the about page to encourage community contribution

[Shelob9]

In the past it has been discussed adding a "Contribute" page or something similar to the WordPress admin. In #23348 @nacin said that until there is a "top-dollar entrance/landing page for contributing to all things WordPress" this was a no-go and people agreed. Now that we have ​https://make.wordpress.org/ and it is pretty awesome, I think it's time to re-consider.

I have a patch that adds a "Contribute" tab to the "About" page. It focuses less on contributing to core, and more on other ways to contribute to the project--docs, theme review, accessibility--that are less apparent to those who are new to the idea.

My parch should be considered a draft proposal and while most of its language is lifted from the make site, I'm sure the text will need some revision. That said, I think it's passed time to add this in some form or another and wanted to start the conversation.

[nacin]

In this case, #23348 should be reopened, as there's already discussion there.

[Shelob9]

@nacin #23348 proposed adding a link in the W menu to a contribute page, presumably on WordPress.org, which didn't exist. This ticket propose an alternate approach--adding it as a tab in the about page. That's why I created a new ticket. I referenced the related ticket to give the idea historical context.

[SergeyBiryukov]

I've reopened #23348 and updated the title. Could you please upload your patch there? Thanks!

[Shelob9]

@SergeyBiryukov Fair enough. I have now done so.