Updating CONTRIBUTING.md

Author: PaulZC

CONTRIBUTING.md

@@ -3,12 +3,17 @@
 Thank you so *much* for offering to help out. We truly appreciate it.
 
 If you'd like to contribute, start by searching through the [issues](https://github.com/sparkfun/SparkFun_Ublox_Arduino_Library/issues) and [pull requests](https://github.com/sparkfun/SparkFun_Ublox_Arduino_Library/pulls) to see whether someone else has raised a similar idea or question.
+Please check the [closed issues](https://github.com/sparkfun/SparkFun_Ublox_Arduino_Library/issues?q=is%3Aissue+is%3Aclosed)
+and [closed pull requests](https://github.com/sparkfun/SparkFun_Ublox_Arduino_Library/pulls?q=is%3Apr+is%3Aclosed) too - you may find that your issue or feature has already been discussed.
 
 If you decide to add a feature to this library, please create a PR and follow these best practices:
 
-* Change as little as possible. Do not sumbit a PR that changes 100 lines of whitespace. Break up into multiple PRs if necessary.
+* Change as little as possible. Do not submit a PR that changes 100 lines of whitespace. Break up into multiple PRs if necessary.
 * If you've added a new feature document it with a simple example sketch. This serves both as a test of your PR and as a quick way for users to quickly learn how to use your new feature.
 * If you add new functions also add them to keywords.txt so that they are properly highlighted in Arduino. [Read more](https://www.arduino.cc/en/Hacking/libraryTutorial).
+* **Important:** Please submit your PR using the [release-candidate branch](https://github.com/sparkfun/SparkFun_Ublox_Arduino_Library/tree/release_candidate). That way, we can merge and test your PR quickly without changing the _master_ branch
+
+![Contributing.JPG](./img/Contributing.JPG)
 
 ## Style guide