We need more clear language around author submission and adding new features

[lwasser]

Specifically this is a discussion happening in the rdata package review where the author is making changes in between the package being submitted , accepted and then fast tracked to joss. we need to clarify in our policies that

1. no code changes should be made in between the timing of submitting the package /being accepted and then submitted to JOSS - in the same way that you wouldn't edit an academic paper while it was in active review.
2. that packaging should not submit to us until their API is somewhat stable (i feel like we have / had that language somewhere but i can't find it now.