Fix documentation for OpenID connect clientJWT

[strehle]

hint: we do not support RFC 7523 on server side. will come after PR https://github.com/cloudfoundry/uaa/pull/2932 . We need the index for resolution of iss in case of support of RFC 7523

[cf-gitbot]

We have created an issue in Pivotal Tracker to manage this:

https://www.pivotaltracker.com/story/show/187824588

The labels on this github issue will be updated when the story is started.

[strehle]

Before

After