client: Update comment on MEM parcel.cfg key
client: Update comment on MEM parcel.cfg key

- Update comment on the MEM key to note that it is mandatory in format
version 4

cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr,cmusatyalab/openisr