start with GUIDE

GUIDE.md

+# WIP: Guide for RefinedC developers
+
+This guide has two parts: First, a guide for writing typing rules.
+Second, a style guide for RefinedC development.
+
+## Rule guide
+
+1. `SimplifyHyp` and `SimplifyGoal` rules should match: The
+   information learned by the `SimplifyHyp` rule should be enough to
+   prove the `SimplifyGoal`. Said another way, applying the
+   `SimplifyHyp` instance and then proving `SimplifyGoal` should be
+   equivalent to not using any of the two (except for learning more
+   information).
+
+## Style guide
+
+1. Follow the std++/Iris style.
+2. If there is a typeclass to restrict when a typing rule applies, but
+   it does not contain useful information for proving the typing rule,
+   it should only be on the instance, not the lemma.