Docs: ArrowHelper improvement as per suggestion @WestLangley in #5903.

docs/api/extras/helpers/ArrowHelper.html

@@ -74,7 +74,7 @@
 		<div>
 		length -- The desired length<br />
 		headLength -- The length of the head of the arrow<br />
-		headWidth -- The length of the width of the arrow		
+		headWidth -- The length of the width of the arrow
 		</div>
 		<div>
 		Sets the length of the arrowhelper.
@@ -82,7 +82,7 @@
 
 		<h3>[method:null setDirection]([page:Vector3 dir])</h3>
 		<div>
-		dir -- The desired direction in euler format.
+		dir -- The desired direction. Must be a unit vector.
 		</div>
 		<div>
 		Sets the direction of the arrowhelper.