Change whether the current buffer is read-only.
With prefix argument ARG, make the buffer read-only if ARG is
positive, otherwise make it writable. If buffer is read-only
and `view-read-only' is non-nil, enter view mode.
Do not call this from a Lisp program unless you really intend to
do the same thing as the C-x C-q command, including
possibly enabling or disabling View mode. Also, note that this
command works by setting the variable `buffer-read-only', which
does not affect read-only regions caused by text properties. To
ignore read-only status in a Lisp program (whether due to text
properties or buffer state), bind `inhibit-read-only' temporarily
to a non-nil value.