Update is.md

snippets/is.md

@@ -1,6 +1,6 @@
 ### is
 
-Checks if the provided value is of the specified type.
+Checks if the provided value is of the specified type (doesn't work with literals).
 
 Use the `instanceof` operator to check if the provided value is of the specified `type`.
 
@@ -16,4 +16,10 @@ is(RegExp, /./g); // true
 is(Set, new Set()); // true
 is(WeakMap, new WeakMap()); // true
 is(WeakSet, new WeakSet()); // true
+is(String, ''); // false
+is(String, new String('')); // true
+is(Number, 1); // false
+is(Number, new Number(1)); // true
+is(Boolean, true); // false
+is(Boolean, new Boolean(true)); // true
 ```