Here is a rather brief description, at least covering the very special keyboard shortcuts.
What a pity, that I haven’t been able to find it online so far.
But here it is:
Ruby mode:
Major mode for editing Ruby scripts.
TAB properly indents subexpressions of multi-line
class, module, def, if, while, for, do, and case statements, taking
nesting into account.
The variable ruby-indent-level controls the amount of indentation.
key binding
— ——-
C-c Prefix Command
TAB ruby-indent-line
C-j reindent-then-newline-and-indent
RET newline
ESC Prefix Command
{ ruby-electric-brace
} ruby-electric-brace
C-c , Prefix Command
C-M-a ruby-beginning-of-defun ;; actually …-of-class
C-M-e ruby-end-of-defun
C-M-f ruby-forward-sexp
C-M-b ruby-backward-sexp
C-M-h backward-kill-word
C-M-p ruby-beginning-of-block
C-M-n ruby-end-of-block
C-M-q ruby-indent-exp
C-c , a rspec-verify-all
C-c , t rspec-toggle-spec-and-target
C-c , v rspec-verify