Add a note to README about *_changed? (#689)
Add a note to README about *_changed? (#689)

This was introduced in ab43915b0a69e397288ffaa6d35b8e7217b4f259, but
never mentioned in the README file.

Note that the commit message talks about that `:unless =>
:value_changed?` will make validators not run, even though it's not
checked in the code :)
DavyJonesLocker/client_side_validations,DavyJonesLocker/client_side_validations,DavyJonesLocker/client_side_validations