Feature request: add a key binding to set mark in cursor mode

[QiangF]

I have just discovered this great package. The only way to enter selection via keyboard seems to be pressing shift together with arrow keys. Arrow keys are hard to reach, and I have emacs style binding such as Ctrl-f/b/a/e remapped to the common motion keys via xkeysnail, press shift together with Ctrl-f to start selection doesn't work in this case. It will very nice to have a keybinding for setting the selection region start mark, like ctrl-space in emacs.