Add deprecation warning for compute() -> dispatch()

This will help direct readers who see the console.warn deprecation
messages to the right place. To be removed when the specification
patches land.

index.bs

@@ -962,6 +962,9 @@ When the {{MLContext/[[contextType]]}} is set to [=context type/default=] with t
 </details>
 
 ### {{MLContext/compute()}}  ### {#api-mlcontext-compute}
+
+ISSUE: {{MLContext/compute()}} will be deprecated and removed in favor of <code>[dispatch()](https://github.com/webmachinelearning/webnn/blob/main/mltensor-explainer.md#compute-vs-dispatch)</code>.
+
 Asynchronously carries out the computational workload of a compiled graph {{MLGraph}} on a separate timeline, either on a worker thread for the CPU execution, or on a GPU/NPU timeline for submitting a workload onto the command queue. The asynchronous nature of this call avoids blocking the calling thread while the computation for result is ongoing. This method of execution requires an {{MLContext}} created with {{MLContextOptions}}. Otherwise, it [=exception/throws=] an "{{OperationError}}" {{DOMException}}.
 
 <div class="note">