docker (demo): fix starting + better UX: - Use the new `wait_for_service` option to be sure that Prosody is launched. - Use the new `init_script_path` option to initiate forums and bookmark a demo room. - Activate MUC service. - Change log formats to make them more readable.

You'll find install instructions in documentation (see doc/installation.rst).

If you need help, come the Libervia official XMPP room: xmpp:libervia@chat.jabberfr.org?join or join us with a web browser via https://chat.jabberfr.org/converse.js/libervia@chat.jabberfr.org