add github workflow for testing build
this tests any push and PR building on many systems and different
configurations for help find regression
build: remove include(GNUInstallDirs)
add of it caused default of CMAKE_INSTALL_SYSCONFDIR to /usr/etc
default of all paths, if not defined, are present, so I think should be
ok and better remove it
Readme: improve requirements part
github: add issues templates for bug report and feature request