Update README and init.rb: add license information and update version…

… to 4.0.0.

README.rdoc

@@ -25,3 +25,10 @@ Follow below steps to migrate from other plugins :
   * Restart your redmine
 
 Ditto {issue_votes}[https://github.com/KohaSuomi/issue_votes]. Run <code>bundle exec rake -T redmine_hearts:migrate_from</code> to check the task name.
+
+== License
+
+* Codes: MIT License.
+* Legacy Icons: famfamfam-silk: {CC-By-2.5}[https://creativecommons.org/licenses/by/2.5/] by Mark James http://www.famfamfam.com/lab/icons/silk/
+* Vector Icons: {Tabler Icons}[https://tabler.io/]: MIT License
+

init.rb

@@ -22,10 +22,12 @@
 require File.expand_path('../lib/redmine_hearts/view_hook.rb', __FILE__)
 
 Redmine::Plugin.register :redmine_hearts do
+  requires_redmine :version_or_higher => '4.2.0'
+
   name 'Redmine Hearts plugin'
   author '@cat_in_136'
   description 'provide intra-Redmine Like/Fav reactions'
-  version '3.0.1'
+  version '4.0.0'
   url 'https://github.com/cat-in-136/redmine_hearts'
   author_url 'https://github.com/cat-in-136/'