feat(doc): add specification (#723)

* feat(doc): add specification

* fixup!

Author: avivkeller

.prettierignore

@@ -12,3 +12,7 @@ out/
 
 # Generated Files
 src/generators/metadata/maps/mdn.json
+
+# The specification uses things that prettier would not
+# approve of, such as bullets with `*`
+docs/specification.md