Add sub array includes in ruby

src/dev/ruby/arrays.md

@@ -1,6 +1,14 @@
-# Check if all array elements are equals
+# Playing with arrays
+
+## Check if all array elements are equals
 
 ```ruby
 arr = [0, 0, 0, 0, 0, 0, 0]
 puts true if arr.uniq.length == 1
 ```
+
+## Array includes a sub array
+
+```ruby
+(subarray & array) == array
+```