[Enhancement] Improve functionnal and admin minimal documentation

[ponceta]

Tested on qwat 1.2.8, it works nice, it also logs all the diffs when upgrading datamodel.

I miss some basic instructions in the README.MD like :

• How to set logging to tables and views (an addendum that it is already activated for all QWAT tables would be nice, since qwat is paying for this)
• How to query logging tables (small example of sql query)
• How to set up the plugin (plugin download, db_connection, ... )
• Simple example of query on the plugin
• How to clear logging data (all, user specific, ...)

[haubourg]

@ponceta We are finishing to port the plugin to QGIS 3. Are you interested in having us solve those issues ?

[ponceta]

About how to set up plugin configuration :

This will be hosted on the QGIS projects using pg history viewer (QGEP / QWAT).