Improve documentation related to execution.

Bug: 121347610 document that NNAPI Execution inputs/outputs and HAL Request inputs/outputs must not be modified

Test: cd hardware/interfaces/neuralnetworks/1.0/vts/functional ; mma
Test: cd hardware/interfaces/neuralnetworks/1.2/vts/functional ; mma

Change-Id: Iac71d6d5ad92a90afd1b6babb7cfa128d7484c64
diff --git a/neuralnetworks/1.0/IPreparedModel.hal b/neuralnetworks/1.0/IPreparedModel.hal
index ecaa7f8..5320050 100644
--- a/neuralnetworks/1.0/IPreparedModel.hal
+++ b/neuralnetworks/1.0/IPreparedModel.hal
@@ -42,6 +42,13 @@
      * execute function. This callback must be provided with the ErrorStatus of
      * the execution.
      *
+     * If the launch is successful, the caller must not change the content of
+     * any data object referenced by 'request' (described by the
+     * {@link DataLocation} of a {@link RequestArgument}) until the
+     * asynchronous task has invoked the callback object. The asynchronous task
+     * must not change the content of any of the data objects corresponding to
+     * 'request' inputs.
+     *
      * If the prepared model was prepared from a model wherein all
      * tensor operands have fully specified dimensions, and the inputs
      * to the function are valid, then the execution should launch