Add issue template picker to point users to eslint-config-xo repo

[fregante]

I noticed that many issues were recently moved to that repo. For someone using XO, there's no indication of this other repo for the first 500 lines of the readme.

Suggestion:

• add issue picker with an external link to eslint-config-xo with instructions on when to open there

[fregante]

It seems that the other repo still tells to open issues here. What's your current preference?

https://github.com/xojs/eslint-config-xo/blob/main/.github/ISSUE_TEMPLATE/config.yml