[krbdev.mit.edu #9134] dns_lookup_realm not documented

<URL: http://kerborg-prod-app-1.mit.edu/rt/Ticket/Display.html?id=9134 >

Is there any specific information you were hoping to find documented in the
relation description?  So far I have come up with the laconic "Indicate
whether DNS TXT records should be used to map hostnames to realm names.  The
default value is false."

I don't want to get into the precise TXT lookups there, as we have those in
realm_config.html along with the details for SRV and URI records.