Document gitbase audit logs and RBAC

[ajnavarro]

[ajnavarro]

@smola do we want something more than this? https://docs.sourced.tech/gitbase/using-gitbase/configuration#user-credentials

[erizocosmico]

@ajnavarro what shall we do with this?

[ajnavarro]

Closing as done: https://docs.sourced.tech/gitbase/using-gitbase/security