Add CONTRIBUTING documentation with a DCO

Requires commit sign-off and documents the meaning of signing off for the
project.

Signed-off-by: Jonathon Anderson <janderson@ciq.com>

CONTRIBUTING.md

@@ -0,0 +1,24 @@
+# Contributing
+
+## Contributor's Agreement
+
+You are under no obligation whatsoever to provide any bug fixes, patches, or
+upgrades to the features, functionality or performance of the source code
+("Enhancements") to anyone; however, if you choose to make your Enhancements
+available either publicly, or directly to the project, without imposing a
+separate written license agreement for such Enhancements, then you hereby grant
+the following license: a non-exclusive, royalty-free perpetual license to
+install, use, modify, prepare derivative works, incorporate into other computer
+software, distribute, and sublicense such enhancements or derivative works
+thereof, in binary and source code form.
+
+## Getting Started
+
+When contributing to Warewulf, it is important to properly communicate the gist
+of the contribution. If it is a simple code or editorial fix, simply explaining
+this within the GitHub Pull Request (PR) will suffice. But if this is a larger
+fix or Enhancement, you are advised to first discuss the change with the
+project leader or developers.
+
+All commits must be "Signed-off" by using `git commit -s`, acknowledging that
+you agree to the [Developer Certificate of Origin](DCO.txt).