This command searches for a channel.xml first at a secure https and then unsecured http address.
Examples:
php pyrus.phar channel-discover pear.example.com
This tries to locate https://pear.example.com/channel.xml and if that fails, http://pear.example.com/channel.xml, then adds the channel to the registry.
Use channel-add to add a local channel.xml to the registry.