Create Readme for ConnectToEngagementHub sample

Author: vidrana

ConnectToEngagementHub/README.md

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+# Connect to Engagement Hub
+
+This sample shows the minimum code required for a Power Virtual Agent client to intercept a handoff activity and connect to an engagement hub to transfer conversation to a live agent.
+## Prerequisites
+
+- [.NET Core SDK](https://dotnet.microsoft.com/download) version 2.1
+
+  ```powershell
+  # determine dotnet version
+  dotnet --version
+  ```
+
+## How to try this sample
+- When an end-user interacts with a PVA bot over Directline, messages are sent to client in the form of activities. 
+- In a dialog, when a node to transfer a chat to a live agent is detected, the activities payload contains a handoff activity that is a trigger to transfer the chat.
+- To detect the handoff activity,
+    1. Clone the repository
+    ```bash
+    git clone https://github.com/microsoft/PowerVirtualAgentsSample.git
+    ```
+    2. Add the HandoffHelper and dependent models on the client to intercept activities payload sent over Directline.
+    
+- This helper detects an event activity with name - handoff.initiate.
+- HandoffHelper also parses conversation context (refer to [HandoffContext.cs](./Handoff/HandoffContext.cs)) and the transcript of the conversation between end-user and bot from the handoff.initiate activity.
+- Conversation context and transcript can then be used to write a custom adapter (based on engagement hub APIs) to transfer the chat to a live agent.
+
+## Further reading
+- [Configure hand-off to any generic engagement hub](https://review.docs.microsoft.com/en-us/power-virtual-agents/configure-generic-handoff)