Add to man page: 0 as prio when -i, -b

[dE <de.techno@gmail.com>]

As we know the batch and idle algorithms don't have priorities. But chrt 
expects '0' as the priority, otherwise the command fails.

# chrt -i cat /etc/fstab

chrt - manipulate real-time attributes of a process

Set policy:
   chrt [options] [<policy>] <priority> [-p <pid> | <command> [<arg>...]]
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# chrt -i 0 cat /etc/fstab
# /etc/fstab: static file system information.
#
# noatime turns off atimes for increased performance (atimes normally aren't
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