improve doc of envvar

Author: rickeylev

docs/environment-variables.md

@@ -42,8 +42,8 @@ doing. This is mostly useful for development to debug errors.
 
 :::{envvar} RULES_PYTHON_DEPRECATION_WARNINGS
 
-When `1`, the rules_python will warn users about deprecated symbols that will
-be removed in the next major `rules_python` version. Defaults to `0`.
+When `1`, the rules_python will warn users about deprecated functionality that will
+be removed in a subsequent major `rules_python` version. Defaults to `0` if unset.
 :::
 
 :::{envvar} RULES_PYTHON_ENABLE_PYSTAR