Going back some time ago, I created a tutorial here on setting up MRL on the Raspberry Pi.
Since then, the version of the Rasbian system has changed along with a lot of updates, and those instruction are now out of date.
Here is a link to a video starting with loading the OS onto a micro SD card and working your way through to getting Manticore running on the Raspberry pi 3.
So sit back and enjoy.
Ray.