Document that mysqlbinlog can be used for point-in-time recovery

The mysqlbinlog documentation does not mention that it can be used for point-in-time recovery:

https://mariadb.com/kb/en/library/mysqlbinlog/

MySQL's documentation has a little bit of information:

https://dev.mysql.com/doc/refman/5.6/en/point-in-time-recovery-positions.html

Our documentation should probably also show how to use it with GTIDs and also link to a page that shows how to use it with mariabackup (i.e. see also MDEV-16907).