Add an example of access token to the docs

A user that was following the APIcast on OpenShift documentation was confused about what Access Token is and used the name instead of the value.
To avoid this, it would be good to add an example of how the real access token looks like.

Also, maybe consider adding a screenshot with the Access Token value on the doc page: https://access.redhat.com/documentation/en-us/red_hat_3scale/2.saas/html/accounts/tokens#using_access_tokens