[chore] fixes and updates to documentation: getting started/ping-pong
- updated mingw windows installation section
- add instructions for initial generation of modellib
- other typos and rewording
- removed modellib src-gen contents from repo
- added src-gen exclude to contents
- changed JRE in classpath of java runtime/modellib projects to Eclipse default, instead of hardcoded Java version
Still open:
- runtime/*/gradle.build zip tasks regenerate and include src-gen, which differs from Ant script used by maven for building org.eclipse.etrice.ui.runtime. Not sure if these should also exclude src-gen?