Add email of project bot users in documentation

The documentation https://docs.gitlab.com/ee/user/project/settings/project_access_tokens.html states how the username of project bots are created, but does not state anything about the email address.

The email however is required to match if the bot should need to push its commits while the push rule is active, which only allows commits from team members.

Please add a line in the documentation, stating that the email is generated as project{project_id}_bot@example.com - mind the missing first underscore in contrast to the username!

Commits can then be made with this config:

git config user.name "{token_name}"
git config user.email "project{project_id}_bot@example.com"