Add reviewing info (exercism#1880)

Co-authored-by: BethanyG <[email protected]>
Co-authored-by: Jeremy Walker <[email protected]>

README.md

@@ -6,6 +6,16 @@ Shared metadata for Exercism exercises.
 
 Please see the [contributing guide](./CONTRIBUTING.md).
 
+## Reviewing Guidelines
+
+Pull Requests to this repo require three approving reviews to be merged.
+
+- If you think that a PR should not be merged, either as is or in general, please leave a review **requesting changes**.
+- Please also use the **Request Changes** button if you are unsure about how a concern of yours could be resolved.
+  - This will block the PR from being merged until the change request has been addressed / overruled by an admin.
+  - It ensures that your thoughts will be heard and can be addressed rather than being overruled by a majority.
+- When a discussion goes stale or there are several opposing views and a compromise cannot be reached, ping [@exercism/maintainers-admin](https://github.com/orgs/exercism/teams/maintainers-admin/members) to resolve the discussion.
+
 ## Exercise Metadata
 
 Each exercise's metadata lives in a directory under `exercises/`.