When I put the following in my gemfile:
gem 'client_side_validations'#, github: 'DavyJonesLocker/client_side_validations'
gem 'client_side_validations-simple_form'#, github: 'DavyJonesLocker/client_side_validations-simple_form'
Bundler could not find compatible versions for gem "rails":
rails (= 5.0.0)
client_side_validations-simple_form was resolved to 3.2.0, which depends on
client_side_validations (~> 4.2.0) was resolved to 4.2.0, which depends on
rails (< 4.3.0, >= 4.0.0)
Rails 5 support is not ready for the
client_side_validations gem. Take a look at this issue #645. You can try experimental branch as suggested in the issue's comment.