UA Help

I need help on how to implement this unique ability. "Double movement when inside your borders" I somewhat new to civ v modding and cannot figure on how to implement this. Thank you for reading this

Hello, LivingLikeLogan.
I am a very newbie of UI modding too, so I can't write a code for you but I will try to provide some ideas.
Is it possible to make a promption of units, which double the movement when in friendly territory, then add this promption to all units own by this civ using a LUA file?