Improved docs for mappings.

[hschletz]

• The instructions for quota and groups were mixed up. They are now separated into distinct paragraphs.
• Added Instructions for role creation/assignment and added a note about the relationship between roles and groups.

[marc-farre]

Thanks.
If it can help, I've successfully synced Keycloak groups this way (I didn't create the custom ownCloudGroups mapper, I create the built in groups mapper instead):

On Keycloak, in the client mappers, add the built in "groups" attribute.
This "groups" attribute must be in the config file, in oidc_login_attributes.
And set 'oidc_create_groups' => true,

On Keycloak, for each group:

• Create a role with the same name (Configure -> Roles)
• Edit the group (Manage -> Groups) -> Roles Mapping: add the role

On Nextcloud, admin group cannot be renamed.
So if you have an admin group called, e.g. Administrators, create the role admin and map it to Administrator group.

[luuksommers]

Thank you, this PR helped me a lot. Please note that when adding a custom mapper, keep the Add to userinfo flag enabled, as the OidcProvider uses the userinfo endpoint to fetch the group information.