Added specifications to README
Context: SWH, Inria and the CCSD (in charge of the HAL's archive) are working on pushing HAL's source code deposit into SWH with SWORD protocol.
This specs were edited by ardumont and myself on the notepad available on: https://pad.riseup.net/p/t4mJsj9RB0OQ
Migrated from D220 (view on Phabricator)