docs: adding request/reply content in module-3

100-level-AsyncAPI-Intro/step2.md

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+## Request/reply 
+As Eve and Chan near the completion of their communication system setup, Eve takes a moment to elaborate on the request/reply pattern to Chan, emphasizing that it is a communication pattern rather than a separate component.
+
+Eve clarifies to Chan that this pattern involves two key roles: a requestor and a replier.
+
+In their setup, they establish a channel named `communication` to facilitate requests and enable communication. Now they can stay in touch and communicate about Eve's adventures and Chan's fascinating discoveries during his intergalactic travels. 
+
+```yml
+asyncapi: 3.0.0
+info:
+  title: Eve And Chan's Communication APP
+  version: 1.0.0
+channels:
+  communication:
+    address: /brownieterra
+    messages:
+      chit_chat:
+        payload:
+          type: string
+      cool_discovery:
+        payload:
+          type: object
+          properties:
+            title:
+              type: string
+            info:
+              type: string
+            date:
+              type: string
+      confirmation:
+        payload:
+          type: boolean
+operations:
+  sendChit_Chat:
+    action: send
+    channel:
+      $ref: "#/channels/communication"
+    messages:
+      - $ref: "#/channels/communication/messages/chit_chat"
+    reply:
+      channel:
+        "$ref": '#/channels/communication'
+      messages:
+       - $ref: "#/channels/communication/messages/chit_chat"
+  sendDiscovery:
+    action: send
+    channel:
+      $ref: "#/channels/communication"
+    messages:
+      - $ref: "#/channels/communication/messages/cool_discovery"
+    reply:
+      channel:
+        "$ref": '#/channels/communication'
+      messages:
+       - $ref: "#/channels/communication/messages/confirmation"
+```
+
+Chan wonders how Eve could reach him if he travels around and his address(reply address) is unknown. 
+
+Eve teaches Chan how to set up a communication system and stay in touch even when the reply address is not known. 
+
+```yaml 
+channels:
+  communication:
+    address: /brownieterra
+    messages:
+      chit_chat:
+        payload:
+          type: string
+      cool_discovery:
+        payload:
+          type: object
+          properties:
+            title:
+              type: string
+            info:
+              type: string
+            date:
+              type: string
+      confirmation:
+        payload:
+          type: boolean
+  secret_channel:
+    address: /cappucinova
+    messages:
+      secret_stuff:
+        payload:
+          type: string
+operations:
+  sendSecretMessage:
+    action: send
+    channel:
+      "$ref": "#/channels/secret_channel"
+    reply:
+      address:
+        "description": "Consumer inbox"
+        "location": "$message.header#/secret_reply_channel"
+  sendChit_Chat:
+    action: send
+    channel:
+      $ref: "#/channels/communication"
+    messages:
+      - $ref: "#/channels/communication/messages/chit_chat"
+    reply:
+      channel:
+        "$ref": '#/channels/communication'
+      messages:
+       - $ref: "#/channels/communication/messages/chit_chat"
+  sendDiscovery:
+    action: send
+    channel:
+      $ref: "#/channels/communication"
+    messages:
+      - $ref: "#/channels/communication/messages/cool_discovery"
+    reply:
+      channel:
+        "$ref": '#/channels/communication'
+      messages:
+       - $ref: "#/channels/communication/messages/confirmation"
+```
+
+With the final pieces programmed and the communication system in place, Chan gets ready to return home. 
+
+Making a promise to stay in touch, Chan takes off in his spaceship back to Brownieterra.