#128 document configuring w/o sql backend

[t_mk1]

Some use cases exist where it might not be desirable to report on DMARC, for any verified traffic.

For this purpose I suggest that the use of --without-sql-backend be better described and documented, at least in the INSTALL file.
Beyond that configure-time option, is there anything else that should change in the default configuration in that instance? Automatic updates to accommodate, or further instructions

[Murray S. Kucherawy]

Done for 1.4.0.