Add contact and issue report section.

CONTRIBUTING.md

@@ -5,6 +5,20 @@ Dubbo is released under the non-restrictive Apache 2.0 license, and follows a ve
 ### Sign the Contributor License Agreement
 Before we accept a non-trivial patch or pull request we will need you to sign the Contributor License Agreement. Signing the contributor’s agreement does not grant anyone commit rights to the main repository, but it does mean that we can accept your contributions, and you will get an author credit if we do. Active contributors might be asked to join the core team, and given the ability to merge pull requests.
 
+### Contact
+
+#### Mailing list
+
+The mailing list is the recommended way for discussing almost anything that related to Dubbo. Please refer to this [guide](https://github.com/apache/incubator-dubbo/wiki/Mailing-list-subscription-guide) for detailed documentation on how to subscribe.
+
+- [dev@dubbo.incubator.apache.org](mailto:dev-subscribe@dubbo.incubator.apache.org): the develop mailing list, you can ask question here if you have encountered any problem when using or developing Dubbo.
+- [commits@dubbo.incubator.apache.org](mailto:commits-subscribe@dubbo.incubator.apache.org): all the commits will be sent to this mailing list. You can subscribe to it if you are interested in Dubbo's development.
+- [notification@dubbo.incubator.apache.org](mailto:notification-subscribe@dubbo.incubator.apache.org): all the Github [issue](https://github.com/apache/incubator-dubbo/issues) updates and [pull request](https://github.com/apache/incubator-dubbo/pulls) updates will be sent to this mailing list.
+
+### Reporting issue
+
+Please follow the [template](https://github.com/apache/incubator-dubbo/issues/new?template=dubbo-issue-report-template.md) for reporting any issues.
+
 ### Code Conventions
 Our code style is almost in line with the standard java conventions (Popular IDE's default setting satisfy this), with the following additional restricts:  
 * If there are more than 120 characters in current line, start a new line.
@@ -46,7 +60,6 @@ git push origin your_awesome_patch
 
 Thanks for contributing!
 
-
 ### Code style
 
 We provide a template file [dubbo_codestyle_for_idea.xml](https://github.com/apache/incubator-dubbo/tree/master/codestyle/dubbo_codestyle_for_idea.xml) for IntelliJ idea, you can import it to you IDE.