Update documentation for Shared API Gateway

Author: vlewin

README.md

@@ -178,8 +178,10 @@ service: service-name
 provider:
   name: aws
   apiGateway:
-    restApiId: xxxxxxxxxx # REST API resource ID. Default is generated by the framework
-    restApiRootResourceId: xxxxxxxxxx # Root resource, represent as / path
+    # REST API resource ID. Default is generated by the framework
+    restApiId: xxxxxxxxxx 
+    # Root resource, represent as / path
+    restApiRootResourceId: xxxxxxxxxx 
 
 functions:
   ...
@@ -194,14 +196,25 @@ provider:
   apiGateway:
     restApiId: xxxxxxxxxx
     restApiRootResourceId: xxxxxxxxxx
-    restApiResources: # List of existing resources that were created in the REST API. This is required or the stack will be conflicted
-
-      /posts: xxxxxxxxxx
+    # List of existing resources that were created in the REST API. This is required or the stack will be conflicted
+    restApiResources: 
+      /users: xxxxxxxxxx
 
 functions:
   ...
 ```
 
+Now we can define endpoints using existing API Gateway ressources
+
+```yml
+stepFunctions:
+  stateMachines:
+    hello:
+      events:
+        - http:
+            path: users/create
+            method: POST
+```
 
 #### Enabling CORS