Update issue_template.md to notify users to use JIRA to open a new issue

Author: nfalco79

.github/issue_template.md

@@ -1,26 +1,3 @@
-<!--
-User question must be directed at the Jenkins user mailing list or Jenkins gitter
-https://groups.google.com/group/jenkinsci-users/topics
-https://gitter.im/jenkinsci/jenkins
-Only concerned about actual issues or features regarding the plugin, these features are best sent a pull request.
-Be warned that issues regarding user question will be closed.
--->
+Please report new issue of this plugin to JIRA issue tracker at https://issues.jenkins.io rather than GitHub.
 
-### Your checklist for this issue
-
-- [ ] Jenkins version
-
-- [ ] Plugin version
-
-- [ ] Bitbucket cloud
-
-- [ ] Bitbucket server and version
-
-<!--
-Put an `x` into the [ ] to show you have filled the information below
-Describe your issue below
--->
-
-### Description
-
-Please describe your issue here.
+More information at https://github.com/jenkinsci/bitbucket-branch-source-plugin/blob/master/README.md#issue-tracking-where-file-new-issues.