[otbn] Documentation for existing V1 progress
[otbn] Documentation for existing V1 progress

This updates the checklist for what's been done so far: there are
still some jobs to do.

Signed-off-by: Rupert Swarbrick <290093e2ad2515ed2f14d749293c8cf8e02ca274@lowrisc.org>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan