Update the auth_to_local rules documentation in hadoop documentation

<property>
<name>hadoop.security.auth_to_local</name>
<value>
RULE:[2:$1@$0](nn/.@.*REALM.TLD)s/./hdfs/
RULE:[2:$1@$0](jn/.@.*REALM.TLD)s/./hdfs/
RULE:[2:$1@$0](dn/.@.*REALM.TLD)s/./hdfs/
RULE:[2:$1@$0](nm/.@.*REALM.TLD)s/./yarn/
RULE:[2:$1@$0](rm/.@.*REALM.TLD)s/./yarn/
RULE:[2:$1@$0](jhs/.@.*REALM.TLD)s/./mapred/
DEFAULT
</value>
</property>

As the first part is translating to nn@REALM, so the expression is not matching, and the replacement is not happening.