added document for 0.6.0 mongodb migration
added document for 0.6.0 mongodb migration

nbargnesi/openbel-server,OpenBEL/openbel-server,nbargnesi/openbel-server,OpenBEL/openbel-api,OpenBEL/openbel-server,OpenBEL/openbel-api,OpenBEL/openbel-server,nbargnesi/openbel-server,OpenBEL/openbel-api,OpenBEL/openbel-api