Added integration tests readme.

tests/Avalonia.IntegrationTests.Appium/readme.md

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+# Running Integration Tests
+
+## Windows
+
+### Prerequisites
+
+- Install WinAppDriver: https://github.com/microsoft/WinAppDriver
+
+### Running
+
+- Run WinAppDriver (it gets installed to the start menu)
+- Run the tests in this project
+
+## MacOS
+
+### Prerequisites
+
+- Install Appium: https://appium.io/
+- `cd samples/IntegrationTestApp` then `./bundle.sh` to create an app bundle for `IntegrationTestApp`
+- Register the app bundle by running `open -n ./bin/Debug/net6.0/osx-arm64/publish/IntegrationTestApp.app` 
+
+### Running
+
+- Run `appium`
+- Run the tests in this project
+
+Each time you make a change to Avalonia or `IntegrationTestApp`, re-run the `bundle.sh` script (registration only needs to be done once).
+
+