Docs live version updated

Author: Elise-Kaminski

readme.md

@@ -7,6 +7,6 @@ If you want to contribute, please read our [contribution guide](https://os.mbed.
 Please open pull requests against either:
 
 - `development` - this is our development branch.
-- `6.15` - this is the latest live version.
+- `6.16` - this is the latest live version.
 
 Older version branches probably don't require fixes; please open an issue if you think we're wrong.