docs: add file uploads (#4626)

Co-authored-by: Geoffroy Couprie <apollo@geoffroycouprie.com>
Co-authored-by: Edward Huang <edward.huang@apollographql.com>
Co-authored-by: Bryn Cooke <BrynCooke@gmail.com>
Co-authored-by: Jesse Rosenberger <git@jro.cc>