Initial contributor guide (#1010)

* Initial contributor guide

* Update CONTRIBUTING.md

Co-authored-by: Daniël van Eeden <[email protected]>

---------

Co-authored-by: lance6716 <[email protected]>

Author: dveeden

CONTRIBUTING.md

@@ -0,0 +1,17 @@
+# How to contribute
+
+## Your first contribution
+
+- Best to first create an issue and discuss the problem and possible solution.
+  - This isn't needed for small/obvious fixes.
+  - What is the context? e.g. what versions of go-mysql, MySQL, etc does this apply to?
+  - Do you have a simple test case? This can just be example code, it doesn't have to be a full test case.
+  - Why do you need this change?
+- Format your code with [gofumpt](https://github.com/mvdan/gofumpt) if possible. (`make fmt` does this for you)
+- Reference an issue in the PR if you have one.
+- Update the `README.md` if applicable.
+- Add tests where applicable.
+
+## Asking for help
+
+- Don't be afraid to ask for help in an issue or PR.