Add guidelines in Protein Complex creation box

[pgaudet]

Please add this comment on the Protein Complex creation box

Note that this should be used rarely, and only in the case where the activity cannot be ascribed to a single subunit of a complex (see GO guidelines for “contributes to” annotations).

Can you link to https://wiki.geneontology.org/Contributes_to?

@vanaukenk @cmungall @thomaspd

[tmushayahama]

@pgaudet Now on production