contrib guide

CONTRIBUTION_GUIDE.md

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+# Contribution guide
+
+## Trust the process
+
+Up until recently, `migra` had a very laissez-faire approach to contributions, but that created a few issues that made it harder for maintainers to review and left PRs languishing for too long.
+
+This new contributions guidelines are aimed to fix that, while still making contributing easy and approachable.
+
+Make sure your contribution follows these steps:
+
+- Before getting into code, raise an issue - maintainers should have useful advice on how to approach the change. Build some basic consensus on the approach before coding.
+
+- Break the fix/feature/change into several smaller changes. Most changes will also involve changing `schemainspect` at the same time, which does most of the gruntwork under the hood of migra.
+
+- Keep the individual PRs extremely small. 100 lines or less ideally. This one is key for making them quick and easy to review.
+
+## Meet the maintainers
+
+Your humble team of maintainers currently consists of the following folks:
+
+- @djrobstep (original author)
+- @maximsmol, @kennyworkman, @aidanabd (new volunteers from latch.bio)
+