Add review policy doc

This documents various attributes of our overall review policy from code,
design, and product perspectives.

Fixes #12614

docs/review.md

@@ -0,0 +1,67 @@
+# Review Guidelines
+
+The following summarises review guidelines that we follow for pull requests in
+Riot Web and other supporting repos. These are just guidelines (not strict
+rules) and may be updated over time.
+
+## Code Review
+
+When reviewing code, here are some things we look for and also things we avoid:
+
+### We review for
+
+* Correctness
+* Performance
+* Accessibility
+* Security
+* Comments and documentation where needed
+* Sharing knowledge of different areas among the team
+* Ensuring it's something we're comfortable maintaining for the long term
+
+### We should avoid
+
+* Style nits that are already handled by the linter
+* Dramatically increasing scope
+
+### Good practices
+
+* Use empathetic language
+  * See also [Mindful Communication in Code
+    Reviews](https://kickstarter.engineering/a-guide-to-mindful-communication-in-code-reviews-48aab5282e5e)
+    and [How to Do Code Reviews Like a Human](https://mtlynch.io/human-code-reviews-1/)
+* Authors should prefer smaller commits for easier reviewing and bisection
+* Reviewers should be explicit about required versus optional changes
+  * Reviews are conversations and the PR author should feel comfortable
+    discussing and pushing back on changes before making them
+* Core team should lead by example through their tone and language
+* Take the time to thank and point out good code changes
+* Using softer language like "please" and "what do you think?" goes a long way
+  towards making others feel like colleagues working towards a common goal
+
+### Workflow
+
+* Avoid force pushing to a PR after first round of review
+* Use merge commits when landing
+* PR author merges after review (assuming they have write access)
+* Assign issues only when in progress (don’t overly assign things so it’s clear
+  that anyone on the team can pick up)
+
+## Design and Product Review
+
+We want to ensure that all changes to Riot fit with our design and product
+vision. We often request review from those teams so they can provide their
+perspective.
+
+In more detail, our usual process for changes that affect the UI or alter user
+functionality is:
+
+* For changes that will go live when merged, always flag Design and Product
+  teams as appropriate
+* For changes guarded by a feature flag, Design and Product review is not
+  required (though may still be useful) since we can continue tweaking
+
+As it can be difficult to review design work from looking at just the changed
+files in a PR, authors should be prepared for Design and / or Product teams to
+request a link to an ad-hoc build of Riot (hosted anywhere) that can be used for
+the review. In the future, we [hope to automate
+this](https://github.com/vector-im/riot-web/issues/12624) for every PR.