Definition of done: add copy spelling/grammar/pluralization

Since we don't all agree the pluralization is a given: https://github.com/barsoom/auctionet/commit/9d51c4b63be529bfd2f5f1ad7343fce78d010dc6#commitcomment-7958265
Spelling/grammar/pluralization in DoD for public only

We don't all agree that it's always worthwile for admin pages, see discussion: https://github.com/barsoom/devbook/pull/20
Merge pull request #20 from barsoom/pluralize

Definition of done: add copy spelling/grammar/pluralization to public