Add note about negative indices. fixes webmachinelearning#484

index.bs

@@ -2721,7 +2721,7 @@ partial interface MLGraphBuilder {
 </div>
 
 <div class="note">
- The {{MLGraphBuilder/gather(input, indices, options)/indices}} parameter to {{MLGraphBuilder/gather()}} can not be clamped to the allowed range when the graph is built. Implementations can introduce {{MLGraphBuilder/clamp()}} in the compiled graph if the required clamping behavior is not provided by the underlying platform.
+ The {{MLGraphBuilder/gather(input, indices, options)/indices}} parameter to {{MLGraphBuilder/gather()}} can not be clamped to the allowed range when the graph is built. Implementations can introduce {{MLGraphBuilder/clamp()}} in the compiled graph if the required clamping behavior is not provided by the underlying platform. Similarly, if the underlying platform does not support negative indices, the implementation can introduce operations in the compiled graph to transform a negative index from the end of the dimension into a positive index.
 </div>
 
 <details open algorithm>