Supplement: Localization and broadband follow-up of the gravitational-wave transient GW150914

19 pages, 1 table, submitted to ApJS, see paper for full list of authors.; International audience; This Supplement provides supporting material for arXiv:1602.08492 . We briefly summarize past electromagnetic follow-up efforts as well as the organization and policy of the current electromagnetic follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the electromagnetic follow-up observations that were performed in the different bands.