Not a good idea to use a world-writable directory, see ssh_config(5)…

Note that variable expansion is only available in OpenSSH 8.4 and later,
cf. https://bugzilla.mindrot.org/show_bug.cgi?id=3140 .

This is shorter and more future-proof.  Quoting the manual:

    restrict

        Enable all restrictions, i.e. disable port, agent and X11
        forwarding, as well as disabling PTY allocation and execution of
        ~/.ssh/rc.  If any future restriction capabilities are added to
        authorized_keys files they will be included in this set.

Note that this won't work with Jessie's OpenSSH server.

In particular, move manpages to the 'doc' directory, and generate HTML
documentation  with `make html`.