Add info to docs

Change tub select label against toggle button to allow not creating a new directory, i.e. call rsync pi@donkeypi:~/mycar/data/ instead of rsync pi@donkeypi:~/mycar/data. The latter command will create a new data/ folder within the target data/ folder which we don't want.

Fix ui issues: check for existing config entries in ssh poll and correct path to start screen image.