Update contributing to cover branch strategy.

Author: objcode

CONTRIBUTING.md

@@ -18,6 +18,8 @@ accept your pull requests.
 
 ## Contributing A Patch
 
+All development is done on the `develop` branch. You should base any changes from this branch.
+
 1. Submit an issue describing your proposed change to the repo in question.
 1. The repo owner will respond to your issue promptly.
 1. If your proposed change is accepted, and you haven't already done so, sign a
@@ -28,4 +30,4 @@ accept your pull requests.
    [Kotlin Style Guide](https://android.github.io/kotlin-guides/style.html) for the
    recommended coding standards for this organization.
 1. Ensure that your code has an appropriate set of unit tests which all pass.
-1. Submit a pull request.
+1. Submit a pull request targeting the `develop` branch.