Add DCO (#978)

Add developer certificate of origin

.github/PULL_REQUEST_TEMPLATE/pull_request_template.md

@@ -0,0 +1,7 @@
+## Description:
+
+
+## Checklist:
+  - [ ] The pull request is done against the latest development branch
+  - [ ] Only one feature/fix was added per PR and the code change compiles without warnings
+  - [ ] I accept the [DCO](https://github.com/1technophile/OpenMQTTGateway/blob/development/docs/participate/development.md#developer-certificate-of-origin).