Update ArrayInPlaceManipulationTaintStep documentation

Author: Napalys

javascript/ql/lib/semmle/javascript/Arrays.qll

@@ -447,6 +447,7 @@ private module ArrayLibraries {
 
   /**
    * A taint propagating data flow edge arising from in-place array manipulation operations.
+   * The methods return the pointer to `this` array as well.
    */
   private class ArrayInPlaceManipulationTaintStep extends TaintTracking::SharedTaintStep {
     override predicate heapStep(DataFlow::Node pred, DataFlow::Node succ) {