Add guide back to mapper.txt

[JeodC]

This enables the use of the home button in gptokeyb for devices that have one like the retroid pocket.

[r3claimer]

I removed this for a reason but I am trying to remember why:

cfff4e5

[JeodC]

I removed this for a reason but I am trying to remember why:

cfff4e5

It was somehow broken in the past: https://discord.com/channels/1122861252088172575/1122861253287739534/1202210746591612979

I put it back manually to test out the home button on the rpmini and it seems fine there. Maybe it was a unique bug to the x55.

[JeodC]

I vaguely recall "back = esc" being broken on the doom 3 port and some others in the past, and removing this fixed it.

Works fine now on the rpmini though.