add units to settings menu

[srimanachanta]

the settings menu doesn't indicate that you need to use meters for the bot width and length, people need to look through docs to find this information

[PatribotsProgramming]

Would it be more beneficial for PathPlanner to have a setting to toggle between imperial and metric unit types? For it to need to be clarified across the app would suggest that it may not be metric if not specified, or, that it could change.