Improve warning message

Co-authored-by: Brian Cristante <33549821+brcrista@users.noreply.github.com>

src/setup-python.ts

@@ -55,7 +55,7 @@ async function run() {
       }
     } else {
       core.warning(
-        "Step input 'python-version' is not set, the OS native python version will be used"
+        "The `python-version` input is not set.  The version of Python currently in `PATH` will be used."
       );
     }
     const matchersPath = path.join(__dirname, '../..', '.github');