Update README.md

Add details for modifying the data source

Author: jasonmoodie

README.md

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 # Using Power BI with GitHub Copilot Metrics API
+With the release of the [GitHub Copilot Metrics API](https://github.blog/changelog/2024-04-23-github-copilot-metrics-api-now-available-in-public-beta/) many teams are looking to leverage this data to help monitors usahe against their KPIs. For many, the Copilot Metrics Viewer ([github-copilot-resources/copilot-metrics-viewer](https://github.com/github-copilot-resources/copilot-metrics-viewer)) might be a great option. 
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+However, many organizations that we work with already have established Power BI teams. If your organizations is **already using Power BI read on!**
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+Located in the  `./samples` directory you'll find sample JSON and PBIX files used to create the dashboar below.
 
 ![Image of a Power BI dashboard with GitHuub Copilot Metrics API data displayed.](https://github.com/jasonmoodie/pbi-4-ghcopilot/blob/main/assets/Sample_PBI.png)
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+## Modify the data source
+> Note: This example provided a proof of concept for loading metrics data and requires an exported JSON file. If you have access to the REST API you can configure the Source accordingly.
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+1. Download and open the sample `GitHub Copilot - Telemetry Sample (DM).pbix` file
+2. The file contains three data sources on the right hand side.
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+| Name                  | Description                                            |
+| :-------------------- | :----------------------------------------------------- |
+| GH Copilot - Details  | Detailed breakdown of metrics data by language and editor. |
+| GH Copilot - Summary  | Daily summary of metrics data.                       |
+| Last Refresh          | Used to display the data time of data refresh on the top-right corner of the dashboard. |
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+3. Open the Power Query Editor by right clicking the `GH Copilot - Details` and selecting **Edit query**. 
+4. Modify the **Source** step by click the setting icon, selecting your JSON file and clicking **OK**.
+![Image of a data source selector in Power Query Editor.](https://github.com/jasonmoodie/pbi-4-ghcopilot/blob/main/assets/Modify_JSON_source.png)
+5. Repeat steps 3 and 4 for the `GH Copilot - Summary` Source.
+6. Click **Close and Apply** in the top-left of the Power Query Editor.
+7. On the Report View page click **Refresh** to load the new data into your dashboard.
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