Gatsby: Clarify docs on submitting sites to the showcase

[m-allanson]

Summary

Update the site showcase guidelines at https://github.com/gatsbyjs/gatsby/blob/master/docs/docs/site-showcase-submissions.md

I wasn't sure if the featured flag was supposed to be set to indicate that I would like to be featured, or leave it up to your team.

Based on feedback in #6265.

Motivation

It should be clear how to submit a site to the showcase.

[calebsylvest]

I can take this task on.

Problem

And clear for _whom_ sets the featured flag. I bold/italicized the text that causes confusion

Note on Featured Sites

...

_Please mention here if you think the site you're submitting ought to be featured and why (which of the above criteria apply). If, during the quarterly review process, your site gets selected to be featured, you'll need to change the fields below:_
...

---

TODO

• [x] How should a submission be notated that the poster would like it to be featured?
  
  
  
  • @m-allanson can you answer this question?
  
  
• [x] Add notation that featured should be set to false when posting

Recommended Re-write

## Note on Featured Sites

Featured sites are chosen by Gatsby team the first week of every quarter based on the following criteria:

- wide-reach (site is very popular)
- prestige (creator, content, or company is very well-known)
- unique use case
- unique design

_Note: when posting leave `featured` set to `false`_

### How to Feature a Site
1.  Change `featured: false` to `featured: true`
2.  Add "featured" as a category:

[m-allanson]

@calebsylvest that is a good question... I don't think we have it worked out yet:

How should a submission be notated that the poster would like it to be featured?

@shannonbux @jlengstorf (or anyone else!) any thoughts on this?

[jlengstorf]

Would it make sense to assume that most people submitting a site would like to have it featured?

I think we should default to, "This site will be reviewed by the Gatsby Site Review Board as a candidate for the 'Featured Sites' section of the showcase. If you _do not_ want your site to be featured, please add 'DO NOT FEATURE' to the pull request."

That way there's an opt-out, but we're not burdening every PR with an extra box to check that will most likely _always_ be checked (if publicity is a problem, the site most likely won't be submitted in the first place).

Does that seem reasonable?

[shannonbux]

Also, I like "Gatsby Site Review Board" because it can allow for changes; for example, if the entire community votes get combined with the selection process of a smaller group of people.

[shannonbux]

I updated the doc according to both of your suggestions, shall I close this issue?

@m-allanson @jlengstorf