[Documentation] Differences to ocra?

[rubyFeedback]

Today I found this project via ruby-reddit.

I know ocra a bit but not ruby-packer yet. Would it be possible to
briefly explain differences between the two? I assume ocra is
more platform-limited, but it would be nice to read an official
explanation. Does not have to be long; a short paragraph
should easily suffice, just for people to get a quick overview.

This can be in the main README or just a link to somewhere
else.