Add more information to the documentation about how api/mydata/retrieve is called

[Mohsen Jafari]

It should be mentioned in the documentation that we can send more than one role_ids or published_states to this endpoint like this example:

http://localhost:8080/api/mydata/retrieve?dvobject_types=Dataset&role_ids=6&role_ids=34&published_states=In+Review&published_states=Published&published_states=Unpublished&published_states=Draft&selected_page=1

See also https://dataverse.zulipchat.com/#narrow/stream/378866-troubleshooting/topic/.E2.9C.94.20MyData.20API