Clarify meaning in readme

[LukeIGS]

According to the readme, the versions file and the info file should be "consistently ordered" by the user, however it seems that the versions list returned by rubygems.org doesn't respect any obvious ordering, except maybe the order in which the gem was added to rubygems.org. What does consistent ordering mean?

[simi]

I have shared my understanding of versions file at rubygems/rubygems.org#3904 (comment).