update README.rdoc and welcome PR

Author: cat-in-136

README.rdoc

@@ -5,6 +5,9 @@ Scheduling Poll is a plugin which provides simple polls to scheduling appointmen
 {<img src="https://travis-ci.org/cat-in-136/redmine_scheduling_poll.svg?branch=master" alt="Build Status" />}[https://travis-ci.org/cat-in-136/redmine_scheduling_poll]
 {<img src="https://img.shields.io/redmine/plugin/stars/redmine_scheduling_poll.svg" alt="Redmine Plugins" />}[https://www.redmine.org/plugins/redmine_scheduling_poll]
 
+* belongs to issue (not project)
+* anybody can add alternative date
+
 == How to install
 
 * Download the plugin to your 'plugins/' directory
@@ -15,8 +18,12 @@ Scheduling Poll is a plugin which provides simple polls to scheduling appointmen
 * Go to Admin/Role
 * Add permission "View scheduling polls" and/or "Vote scheduling polls" to some user
 
+== Contributing
 
-== Developing Note
+Bug reports and pull requests are welcome on GitHub at https://github.com/cat-in-136/redmine_scheduling_poll
+
+== License
+
+MIT License.
+See the 'LICENSE.md' file.
 
-* belongs to issue (not project)
-* anybody can add alternative date