F1-m translates to "C-h m", which is the standard Emacs command to show information about the current major-mode. It's not specific to nov.el.
Go emacs!
C-h a - apropos
C-h k <key sequence> - detailed docs on the command run by key sequence
C-h m - docs on current minor modes and major mode
C-h w <command> - what keystrokes will run command
There's a lot more as well.