fix error in README about deploy to staging
fix error in README about deploy to staging

should be: cap staging db:remote_db_upload

Also removed documentation for older cap task no 
longer needed:

cap staging convert:wrap_orphaned_activities_in_investigations

concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse,concord-consortium/rigse