Add key format of #2275 as requirement to CONTRIBUTING.md
Add key format of #2275 as requirement to CONTRIBUTING.md

[ciskip]

shitikanth/jabref,JabRef/jabref,bartsch-dev/jabref,bartsch-dev/jabref,grimes2/jabref,Mr-DLib/jabref,oscargus/jabref,tobiasdiez/jabref,bartsch-dev/jabref,mredaelli/jabref,mredaelli/jabref,zellerdev/jabref,grimes2/jabref,bartsch-dev/jabref,oscargus/jabref,Siedlerchr/jabref,zellerdev/jabref,jhshinn/jabref,mredaelli/jabref,zellerdev/jabref,bartsch-dev/jabref,zellerdev/jabref,shitikanth/jabref,zellerdev/jabref,jhshinn/jabref,grimes2/jabref,Mr-DLib/jabref,oscargus/jabref,JabRef/jabref,jhshinn/jabref,oscargus/jabref,sauliusg/jabref,sauliusg/jabref,mredaelli/jabref,sauliusg/jabref,Siedlerchr/jabref,tobiasdiez/jabref,JabRef/jabref,mredaelli/jabref,Siedlerchr/jabref,jhshinn/jabref,jhshinn/jabref,tobiasdiez/jabref,shitikanth/jabref,Siedlerchr/jabref,oscargus/jabref,sauliusg/jabref,tobiasdiez/jabref,shitikanth/jabref,shitikanth/jabref,Mr-DLib/jabref,grimes2/jabref,Mr-DLib/jabref,Mr-DLib/jabref,grimes2/jabref,JabRef/jabref