* Add "HELIPORT" resource capability to entitlements

Allows Helmholtz ID users with the resource capability
`urn:geant:helmholtz.de:res:HELIPORT#login.helmholtz.de` to use the
HELIPORT instance. More information can be found here:
https://hifis.net/doc/helmholtz-aai/attributes/#resource-capability-information

* Mention access possibility in README