Fix schema name for logging in README

[sumpfralle]

I noticed the following in v0.15.1:

root@AP-2-76:~# olsrd2 --schema=log.info
    info (list)
    Default value:
    Parameter must be on of the following list:
    'all', 'main', 'logging', 'config', 'plugins', 'subsystems', 'class', 'clock', 'duplicate_set', 'eth_listener', 'ff_dat_metric', 'ff_dat_metric_raw', 'layer2', 'layer2info', 'link_config', 'neighbor_probing', 'netjsoninfo', 'nhdp', 'nhdp_r', 'nhdp_w', 'nhdpinfo', 'nl80211_listener', 'olsrv2', 'olsrv2_r', 'olsrv2_w', 'olsrv2_routing', 'olsrv2info', 'os_fd', 'os_interface', 'os_routing', 'os_system', 'packet_socket', 'rfc5444', 'socket', 'stream_socket', 'systeminfo', 'telnet', 'timer', 'viewer', 'rfc5444_r', 'rfc5444_w'
    Description:
        Set logging sources that display info and warnings
root@AP-2-76:~# olsrd2 --schema=logging.info

Thus the documentation is probably not correct at the moment.

[mathiashro]

Merged documentation update.