release-notes.txt: add 2022.04 release notes
release-notes.txt: add 2022.04 release notes

miri64/RIOT,RIOT-OS/RIOT,ant9000/RIOT,RIOT-OS/RIOT,jasonatran/RIOT,kaspar030/RIOT,kaspar030/RIOT,miri64/RIOT,kYc0o/RIOT,kYc0o/RIOT,ant9000/RIOT,kaspar030/RIOT,jasonatran/RIOT,RIOT-OS/RIOT,ant9000/RIOT,ant9000/RIOT,miri64/RIOT,RIOT-OS/RIOT,kaspar030/RIOT,miri64/RIOT,kYc0o/RIOT,miri64/RIOT,kaspar030/RIOT,kYc0o/RIOT,kYc0o/RIOT,jasonatran/RIOT,jasonatran/RIOT,ant9000/RIOT,jasonatran/RIOT,RIOT-OS/RIOT