Include the Springfox Swagger description part in the CONTRIBUTING.md file

CONTRIBUTING.md

@@ -3,3 +3,14 @@
 ARSnova needs you! If you are interested in helping, please review the guidelines found in our [mobile repository][mobile-repository].
 
 [mobile-repository]: https://github.com/thm-projects/arsnova-mobile/blob/master/CONTRIBUTING.md
+
+## Interactive Documentation of the REST API with Springfox(Swagger)
+
+[Springfox](http://springfox.github.io/springfox/docs/current/) automated JSON API documentation for API's built with Spring and 
+supports both version 1.2 and version 2.0 of the [Swagger Specification](https://github.com/swagger-api/swagger-spec/blob/master/versions/2.0.md#swagger-restful-api-documentation-specification).
+In this case we use the versionn 2.0 of Swagger. 
+
+In the [Swagger Annotation Overview](https://github.com/swagger-api/swagger-core/wiki/Annotations) the most frequently-used Annotions are listed and described.
+
+To see all REST APIs from ARSnova-Backend, you can use the follow Swagger Userinface URL: 
+http://localhost:8080/swagger-ui.html
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