added feature for "git notes edit"

tig is useful tool for viewing daily software updates.
I'd like to take a memo while reading new commits with tig.

default keymap is "T".
It's taken from "notes". but "n", "N", "o", "O", "t" are already taken as keymap.
So I choice "T". 
But I'm not think it as best choice.
It needs more discussion, I think.