maneuversd: Add note about cars requiring resume button press to exit standstill (#33665)

* maneuversd: Set active true when resume pressed

* Revert "maneuversd: Set active true when resume pressed"

This reverts commit 1165270c47.

* Add note

* Update README.md

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Co-authored-by: Shane Smiskol <shane@smiskol.com>

tools/longitudinal_maneuvers/README.md

@@ -20,6 +20,8 @@ Test your vehicle's longitudinal control tuning with this tool. The tool will te
 
 5. Ensure the road ahead is clear, as openpilot will not brake for any obstructions in this mode. Once you are ready, press "Set" on your steering wheel to start the tests. The tests will run for about 4 minutes. If you need to pause the tests, press "Cancel" on your steering wheel. You can resume the tests by pressing "Resume" on your steering wheel. 
 
+   **Note:** For GM cars, it is recommended to hold down the resume button for all low-speed tests (starting, stopping and creep) to avoid the car entering standstill.
+
    ![cog-clip-00 01 11 250-00 01 22 250](https://github.com/user-attachments/assets/c312c1cc-76e8-46e1-a05e-bb9dfb58994f)
 
 6. When the testing is complete, you'll see an alert that says "Maneuvers Finished." Complete the route by pulling over and turning off the vehicle.