The Discovery manual provides that Discovery will find the Sametime service automatically - Unfortunately, this service is not enabled by default.

First enable the webapi in the Notes 8.x client.

In the file:
[Note Program]\framework\rcp\plugin_customization.ini
([Note Program] is the directory where the Notes program is installed)

Please correct this line:
"com.ibm.collaboration.realtime.webapi/startWebContainer = false" - to ".....= true "  and then restart your Notes client.

NOTE:
Just be aware of the licensing rules - we have found out, and had confirmed, that turn on/using an API for Sametime, will cost the full Sametime client licens!