Specifications for making twin graph files for the DT Explorer

In the [quick-start](https://learn.microsoft.com/en-us/azure/digital-twins/quickstart-azure-digital-twins-explorer) tutorial, a spreadsheet named [buildingScenario.xlsx](https://github.com/Azure-Samples/digital-twins-explorer/raw/main/client/examples/buildingScenario.xlsx) was provided as a graph file to be imported in the DT Explorer, along with the JSON models.

Is there any guideline/spec wrt creating such an Excel file, please? I couldn't find any, so far.