Update CONTRIBUTING.md

Author: Stefan Kremser

CONTRIBUTING.md

@@ -1,2 +1,5 @@
 Please only make pull requests to the [testing branch](https://github.com/spacehuhn/esp8266_deauther/tree/testing) to avoid future conflicts.  
 The `testing` branch is merged with `master` on every release. 
+
+**Issues** should contain a detailed description with as much information as possible!  
+Also note that issues are for resolving bugs and not to solve YOUR upload error. Please read the [FAQ](https://github.com/spacehuhn/esp8266_deauther/wiki/FAQ), [README](https://github.com/spacehuhn/esp8266_deauther/blob/master/README.md) and search for similar issues before posting a new one.