[discovery.api] minor clarifications

[Stefan Egli]

Hi all,

I've added two minor clarifications to the discovery.api 1.0.2 and wanted to
FYI you:
* https://issues.apache.org/jira/browse/SLING-4668
* https://issues.apache.org/jira/browse/SLING-4669
Any objections?

Cheers,
Stefan