chore: Add contributing guidelines (#874)

It's helpful for us Coders to align on a common set of style
guidelines. While I'd prefer to automate this, documentation
should get us a lot of the way there!

Please review these thoroughly, as PRs will be checked against it
after merge.

docs/CONTRIBUTING.md

@@ -0,0 +1,32 @@
+# Contributing
+
+## Go Style
+
+Contributions must adhere to [Effective Go](https://go.dev/doc/effective_go). Linting rules should
+be preferred over documenting styles (run ours with `make lint`); humans are error prone!
+
+Read [Go's Code Review Comments Wiki](https://github.com/golang/go/wiki/CodeReviewComments) to find
+common comments made during reviews of Go code.
+
+### No Unused Packages
+
+Coders write packages that are used during implementation. It's difficult to validate whether an
+abstraction is valid until it's checked against an implementation. This results in a larger
+changeset but provides reviewers with an educated perspective on the contribution.
+
+## Review
+
+> Taken from [Go's review philosophy](https://go.dev/doc/contribute#reviews).
+
+Coders value thorough reviews. Think of each review comment like a ticket: you are expected to
+somehow "close" it by acting on it, either by implementing the suggestion or convincing the reviewer
+otherwise.
+
+After you update the change, go through the review comments and make sure to reply to every one. You
+can click the "Done" button to reply indicating that you've implemented the reviewer's suggestion;
+otherwise, click on "Reply" and explain why you have not, or what you have done instead.
+
+It is perfectly normal for changes to go through several round of reviews, with one or more
+reviewers making new comments every time and then waiting for an updated change before reviewing
+again. All contributors, including experienced maintainers, are subject to the same review cycle;
+this process is not meant to be applied selectively or discourage anyone from contribution.

docs/README.md

@@ -64,7 +64,7 @@ $ coder projects update gcp-linux
 
 ## Development
 
-The code structure is inspired by [Basics of Unix Philosophy](https://homepage.cs.uri.edu/~thenry/resources/unix_art/ch01s06.html) and [Effective Go](https://go.dev/doc/effective_go).
+Read the [contributing docs](./CONTRIBUTING.md) for style and review guidelines.
 
 Coder requires Go 1.18+, Node 14+, and GNU Make.