Add section about ActiveSupport's method

Author: fatkodima

README.adoc

@@ -1431,6 +1431,23 @@ pets = %w(cat dog)
 pets.include? 'cat'
 ----
 
+=== `exclude?` [[exclude]]
+
+Prefer Active Support's `exclude?` over Ruby's negated `include?`.
+
+[source,ruby]
+----
+# bad
+!array.include?(2)
+!hash.include?(:key)
+!string.include?('substring')
+
+# good
+array.exclude?(2)
+hash.exclude?(:key)
+string.exclude?('substring')
+----
+
 == Time
 
 === Time Zone Config [[tz-config]]