Currently there is some documentation on creating user rights on Manual:User rights#Adding new rights, but this is explicitly directed at people modifying core or writing extensions. There is some much simpler guidance present on Manual:$wgNamespaceProtection, but it's not clear whether creating a user right is actually this simple, or if this page simply ignores extra necessary or recommended steps. There is probably other documentation of the process scattered across other pages as well.

This documentation should be consolidated better and generalized, with explanations of exactly what steps are required for different situations.