[QGIS-Developer] Development environment setup

[Greg Troxel]

I should also say that a well-documented repository to create containers
that aare useful is a help to building manually, as commented code is
more precise than what is in README, so despite my biases, I think it's
a good thing in general.

In that way a container config repo is somewhat similar to packaging
systems.  I maintain the qgis entry in pkgsrc, which lists the
dependency packages, has some patches, a bunch of CMAKE_CONFIGURE_ARGS,
etc.