docs(license): switch to polyform, add contributing.md

CONTRIBUTING.md

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+# Contributing to the Project
+
+The project is a collection of contributions from both the project leaders and
+community members. There are many ways to contribute, this can include content
+in the project repositories, as well as contributing in public and private
+conversation, assisting users, writing blog posts, and many other ways.
+
+## How contributions are made
+
+Contributions to the project primarily happen in the project source
+repositories, but may also occur in other places, such as discussion forums and
+public and private discourse.
+
+## Contributing content to the Project
+
+In order for the project leaders to manage sustained progress toward the
+project goals and maintain project velocity, focus and quality, the project may
+adjust the license terms over time.
+
+Content contributed to the project must therefore be provided under
+sufficiently liberal terms to allow these operations to proceed unimpeded. As
+such contributions are accepted with the following understanding:
+
+* Contributed content is licensed under the terms of the 0-BSD license
+* Contributors accept the terms of the project license at the time of
+  contribution
+
+By making a contribution, you accept both the current project license terms,
+and that all contributions that you have made are provided under the terms of
+the 0-BSD license.
+
+## Zero-Clause BSD
+
+```
+Permission to use, copy, modify, and/or distribute this software for  
+any purpose with or without fee is hereby granted.
+
+THE SOFTWARE IS PROVIDED “AS IS” AND THE AUTHOR DISCLAIMS ALL  
+WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES  
+OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE  
+FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY  
+DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN  
+AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT  
+OF OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+```