README: Add OBS Notifier to client software

[DmitriySalnikov]

Description

Add OBS Notifier to list of supported client software

Motivation and Context

How Has This Been Tested?

Tested OS(s): Windows

Types of changes

Documentation change

Checklist:

• [x] I have read the Contributing Guidelines.
• [x] All commit messages are properly formatted and commits squashed where appropriate.
• [x] My code is not on master or a release/* branch.
• [x] The code has been tested.
• [x] I have included updates to all appropriate documentation.