Add filter out info (`-`) to issue/PR search documentation

[Julian88Tex]

What article on docs.github.com is affected?

https://docs.github.com/en/free-pro-team@latest/github/managing-your-work-on-github/using-search-to-filter-issues-and-pull-requests

What part(s) of the article would you like to see updated?

• Adding filter out info (-) to search documentation with example: state:open type:issue -author:octocat

Additional information

Attempted to navigate to https://github.com/github/docs-content/issues/new/choose but get a 404.

[welcome]

Thanks for opening this issue. A GitHub docs team member should be by to give feedback soon. In the meantime, please check out the contributing guidelines.

[janiceilene]

This was closed in #1248 🎉