[Maria-docs] improving docs around show slave status

hi, just noted this from irc, we don't have detailed docs around things like seconds_behind_master, etc. compare https://mariadb.com/kb/en/mariadb/show-slave-status/ vs http://dev.mysql.com/doc/refman/5.6/en/show-slave-status.html It might be better than us having to look at the code from time to time cheers, -colin -- Colin Charles, Chief Evangelist, MariaDB Corporation blog: http://bytebot.net/blog/| t: +6-012-204-3201 | Skype: colincharles