Update index.bs

Co-authored-by: Anne van Kesteren <annevk@annevk.nl>

index.bs

@@ -317,7 +317,7 @@ on [=this=]'s [=Sanitizer/configuration=].
 </div>
 
 <div algorithm>
-The <dfn for="Sanitizer" export>getDefault</dfn> method steps are to return the
+The static <dfn for="Sanitizer" export>getDefault</dfn> method steps are to return the
 result of [=get a sanitizer instance from options=] with &laquo;[ "{{SetHTMLOptions/sanitizer}}" &rightarrow; "{{SanitizerPresets/default}}" ]&raquo;
 </div>