Add domain expert guidance

doc/development/code_review.md

@@ -24,6 +24,7 @@ uncovered edge cases.
 The default approach is to choose a reviewer from your group or team for the first review.
 This is only a recommendation and the reviewer may be from a different team.
 However, it is recommended to pick someone who is a [domain expert](#domain-experts).
+If your merge request touches more than one domain (for example, Dynamic Analysis and GraphQL), ask for reviews from two experts. 
 
 You can read more about the importance of involving reviewer(s) in the section on the responsibility of the author below.