Add 'test-tag' tag

## Add tag: test-tag

This PR adds the `test-tag` tag to the model repository.

**Changes:**
- Added `test-tag` to model tags
- Updated from 3 to 4 tags

**Current tags:** play, fake, region:us
**New tags:** play, fake, region:us, test-tag

README.md

@@ -2,4 +2,6 @@
 tags:
 - play
 - fake
----
+- region:us
+- test-tag
+---