Add section about long &. chains

Author: fatkodima

README.adoc

@@ -351,6 +351,20 @@ class User
 end
 user&.zip
 ----
+
+=== Long safe navigation chain [[long-safe-navigation-chain]]
+
+Avoid `&.` chains longer than two.
+
+[source,ruby]
+----
+# bad
+user&.address&.zip
+
+# good
+user.address.zip if user
+----
+
 === Spaces and Braces [[spaces-braces]]
 
 No spaces after `(`, `[` or before `]`, `)`.