Add CONTRIBUTING.md

Author: jayvdb

CONTRIBUTING.md

@@ -0,0 +1,7 @@
+# Contributing
+
+## Pull Request Process
+
+The Pull Request continuous integration will check that the cmake files:
+* have appropriate whitespace according to [`trim`](https://pypi.org/project/trim/)
+* comply with [`cmake-lint`](https://pypi.org/project/cmakelang/) rules

README.md

@@ -2,6 +2,8 @@
 
 Swift's commonly used [CMake](https://cmake.org/cmake/help/latest/guide/tutorial/index.html) modules.
 
+See [CONTRIBUTING.md](CONTRIBUTING.md) for details on the process for submitting pull requests.
+
 # LICENSE
 
 Copyright © 2021 Swift Navigation