Update CHANGELOG and RELEASE_NOTES-HEAD

Using the commit-hook actually worked and prevented my local commit
while enforcing the removal of trailing whitespace!

I also added better USAGE guidelines for the generate-release-notes.sh
script (printed if you invoke it without arguments).

`./src/scripts/updateCHANGELOG.sh` does the work without any arguments.
`./src/scripts/generate-release-notes.sh 43.29.1 HEAD` does the latest
release notes file.

Author: freephile