CONTRIBUTING.md: hint to also search closed PRs for previous work
CONTRIBUTING.md: hint to also search closed PRs for previous work

miri64/RIOT,authmillenon/RIOT,RIOT-OS/RIOT,toonst/RIOT,smlng/RIOT,kYc0o/RIOT,toonst/RIOT,x3ro/RIOT,josephnoir/RIOT,aeneby/RIOT,OlegHahm/RIOT,RIOT-OS/RIOT,miri64/RIOT,jasonatran/RIOT,miri64/RIOT,basilfx/RIOT,OTAkeys/RIOT,jasonatran/RIOT,mtausig/RIOT,miri64/RIOT,OTAkeys/RIOT,OlegHahm/RIOT,aeneby/RIOT,authmillenon/RIOT,OTAkeys/RIOT,x3ro/RIOT,jasonatran/RIOT,mtausig/RIOT,smlng/RIOT,mtausig/RIOT,josephnoir/RIOT,RIOT-OS/RIOT,yogo1212/RIOT,smlng/RIOT,basilfx/RIOT,josephnoir/RIOT,toonst/RIOT,toonst/RIOT,josephnoir/RIOT,OlegHahm/RIOT,authmillenon/RIOT,kYc0o/RIOT,josephnoir/RIOT,RIOT-OS/RIOT,x3ro/RIOT,x3ro/RIOT,ant9000/RIOT,kaspar030/RIOT,ant9000/RIOT,smlng/RIOT,OlegHahm/RIOT,yogo1212/RIOT,kYc0o/RIOT,ant9000/RIOT,yogo1212/RIOT,mtausig/RIOT,kaspar030/RIOT,authmillenon/RIOT,jasonatran/RIOT,kaspar030/RIOT,aeneby/RIOT,yogo1212/RIOT,yogo1212/RIOT,kYc0o/RIOT,basilfx/RIOT,yogo1212/RIOT,OTAkeys/RIOT,mtausig/RIOT,jasonatran/RIOT,kaspar030/RIOT,kYc0o/RIOT,x3ro/RIOT,OlegHahm/RIOT,authmillenon/RIOT,authmillenon/RIOT,smlng/RIOT,aeneby/RIOT,ant9000/RIOT,miri64/RIOT,ant9000/RIOT,OTAkeys/RIOT,aeneby/RIOT,basilfx/RIOT,kaspar030/RIOT,RIOT-OS/RIOT,basilfx/RIOT,toonst/RIOT