Fixed typo and added a little formatting (#290)

CONTRIBUTING.md

@@ -8,18 +8,18 @@ agree to follow the code of conduct below
 Fork, then clone the repo
 
 Make your modification,
-* If you want to add a new gateway, name it ZgatewayXXX, XXX replaced by your gateway communication type, can be more than three letters
-* If you want to add a new sensor, name it ZsensorYYY, YYY replaced by your sensor type, can be more than three letters
-* If you want to add a new actuator, name it ZactuatorZZZ, ZZZ replaced by your actuator type, can be more than three letters
+* If you want to add a new gateway, name it `ZgatewayXXX`, `XXX` replaced by your gateway communication type, can be more than three letters
+* If you want to add a new sensor, name it `ZsensorYYY`, `YYY` replaced by your sensor type, can be more than three letters
+* If you want to add a new actuator, name it `ZactuatorZZZ`, `ZZZ` replaced by your actuator type, can be more than three letters
 
 Review your code, compile it for Arduino Uno and ESP8266
 
 Test it localy on your hardware config
 
-If you modify user_config.f during your developments you need to report your modifications into Test_config.h
+If you modify `User_config.h` during your developments you need to report your modifications into Test_config.h
 https://github.com/1technophile/OpenMQTTGateway/blob/master/tests/Test_config.h 
-Indeed during the continuous integration process user_config.h is replaced by test_config.h. 
-test_config.h as much more gateway/sensors enabled for the test than the default user_config.h
+Indeed during the continuous integration process `User_config.h` is replaced by `Test_config.h`. 
+`Test_config.h` as much more gateway/sensors enabled for the test than the default `User_config.h`
 
 Emit a pull request