FR: Button to perform incremental update

It would be really handy to have a button that performed the following commands:

cd /data/openpilot
git pull
reboot

The built-in updater as well as the updater using workbench clones a new copy and there is that 20-minute build time at startup.

When working on rapidly changing code, this is SO much faster. Would just be convenient to have a button is all.

Thanks!