Updated readme for inference (#31597)

### Packages impacted by this PR
inference.   Only readme

### Issues associated with this PR


### Describe the problem that is addressed by this PR


### What are the possible designs available to address the problem? If
there are more than one possible design, why was the one in this PR
chosen?


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### Checklists
- [ ] Added impacted package name to the issue description
- [ ] Does this PR needs any fixes in the SDK Generator?** _(If so,
create an Issue in the
[Autorest/typescript](https://github.com/Azure/autorest.typescript)
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- [ ] Added a changelog (if necessary)

Author: howieleung

sdk/ai/ai-inference-rest/README.md

@@ -477,7 +477,7 @@ if (connectionString) {
 provider.register();
 ```
 
-In addition, you need to register to use instrumentation for Azure SDK. You must do this before you import any dependency of `@azure-core-tracing`
+To use instrumentation for Azure SDK, you need to register it before importing any dependencies from `@azure/core-tracing`, such as `@azure-rest/ai-inference`.
 
 ```js
 import { registerInstrumentations } from "@opentelemetry/instrumentation";
@@ -486,6 +486,8 @@ import { createAzureSdkInstrumentation } from "@azure/opentelemetry-instrumentat
 registerInstrumentations({
   instrumentations: [createAzureSdkInstrumentation()],
 });
+
+import ModelClient from "@azure-rest/ai-inference";
 ```
 
 Finally when you are making a call for chat completion, you need to include