[QGIS-Developer] Docs/Instructions for Filter/Query Builder

[pathmapper]

>> I've just been asked by some average QGIS user (unknown to SQL 
>> queries) how to create a simple filter like cityname='foo' for a 
>> vector layer.
>> That was almost impossible for that person, unaware of SQL...

Thank you for raising this issue Richard, got the same feedback from 
some users.

For filtering WFS layers with "SQL Query Composer" it could help to 
pre-fill the "Colums" and "Table(s) fields" -> 
https://github.com/qgis/QGIS/issues/42800

But having

>> toggle/tabbed control between "simple" and "SQL builder" or the 
>> like...

as Nyall suggested would be even better.

Cheers,
Björn