Adding documentation to repeat_required.js

src/js/parser/javascript/repeat_required.js

@@ -1,3 +1,7 @@
+// RepeatRequired nodes are used for `a+` regular expression syntax. It is not
+// rendered directly; it just indicates that the [Repeat](./repeat.html) node
+// loops one or more times.
+
 export default {
   minimum: 1,
   maximum: -1