comment why env is empty for pipstar

Author: rickeylev

python/private/pypi/whl_library.bzl

@@ -358,6 +358,8 @@ def _whl_library_impl(rctx):
     enable_pipstar = (rp_config.enable_pipstar or whl_path) and rctx.attr.config_load
     enable_pipstar_extract = enable_pipstar and rp_config.bazel_8_or_later
 
+    # When pipstar is enabled, Python isn't used, so there's no need
+    # to setup env vars to run Python.
     if enable_pipstar_extract:
         environment = {}
     else: