Update system events docs (#34622)

Author: JoshLove-msft

specification/eventgrid/Azure.Messaging.EventGrid.SystemEvents/README.md

@@ -73,9 +73,10 @@ More on `@example` can be found [here](https://typespec.io/docs/standard-library
 
 1) Write your service's system events in TypeSpec.
 1) Generate the swagger for your service's system events off of TypeSpec, following the steps below:
-    - Install TypeSpec `npm install @typespec/compiler`
+    - Install TypeSpec `npm install -g @typespec/compiler`
     - Install the emitter `npm install @azure-tools/typespec-autorest`
     - Under `/Azure.Messaging.EventGrid.SystemEvents/`:
-        - Run `npx tsp compile main.tsp --emit @azure-tools/typespec-autorest`
-1) Verify the generated swagger under `/data-plane/Microsoft.EventGrid/2024-01-01/` accurately depicts your system events and commit it.
+        - Run `tsp compile .`
+1) Verify the generated swaggers `/data-plane/Microsoft.EventGrid/2018-01-01/GeneratedSystemEvents.json` and `/data-plane/Microsoft.EventGrid/2024-01-01/GeneratedSystemEvents.json` accurately depicts your system events.
+1) Copy the delta from `/data-plane/Microsoft.EventGrid/2018-01-01/GeneratedSystemEvents.json` into your resource provider-specific swagger, e.g. `data-plane/Microsoft.Communication/stable/2018-01-01/AzureCommunicationServices.json`. Make any manual adjustments as needed.
 1) Final PR must contain the TypeSpec and the Swagger generated from the TypeSpec.