update CONTRIBUTING.md to explain cosmetics policy

Also adds a blurb about the missing code style guide.

CONTRIBUTING.md

@@ -1,3 +1,21 @@
 Thank you for all the enthusiasm around open-gpu-kernel-modules.
 
-For the next while, we are going to focus review on pull requests of functional changes.  Please refrain from further cosmetic pull requests until we publish our style guide.
+## Non-functional (cosmetic) changes
+
+While we appreciate your enthusiasm, we have decided not to accept non-functional changes such as
+non-code typo fixes, comment and language adjustments, whitespace changes, and similar.
+
+Changes going into this codebase incur significant overhead. As such, we want to focus our resources
+on executable code improvements for now.
+
+If you have questions, or are unsure about the nature of your desired change, please ask us on the
+[Discussion boards](https://github.com/NVIDIA/open-gpu-kernel-modules/discussions)!
+
+## Code style
+
+We currently do not publish a code style guide, as we have many different components coming together.
+Please read the existing code in the repository, especially the one surrounding your proposed change,
+to get a feel for what you should aim for.
+
+Don't worry too much about it! We are happy to guide you through any neccessary style changes through
+code review of your PR.