Add a documentation link in a specific Config page, that is:

Config > Setting > projects.custom-field-definitions

Comparison example:

User	People

This change is a boring follow-up of this one:

https://we.phorge.it/D25507

Visit the page and click on the new link:

• /config/edit/projects.custom-field-definitions/

Visit this page that was the inspirational page:

• /config/edit/user.custom-field-definitions/

Check that no nuclear implosion is raised.