Add a readme for the powershell based end to end tests (#5087)

scripts/e2etests/README.md

@@ -0,0 +1,30 @@
+# NuGet E2E test scripts
+
+This is a collection of scripts for Visual Studio End-to-End tests that run via the Package Manager Console.
+
+The End-to-End tests depend on an integration provided by the [API.Test](./../../test/TestExtensions/API.Test/API.Test.csproj) project and the Package Manager Console's access to Visual Studio services.
+
+The [CreateEndToEndTestPackage.ps1](./../cibuild/CreateEndToEndTestPackage.ps1) script generates a zip file that contains all the details needed for running End-to-End test.
+This zip file can also be generated by the [build.ps1](./../../build.ps1) script.
+Note that the scripts assume certain relative paths that are correct within the zip, but may not work if you attempt to use the scripts from the repo location.
+
+***NOTE:*** To ensure that all tests are runnable, you may need to update Visual Studio with [tests vs config](build\tests.dev17.vsconfig).
+
+## Running the tests
+
+These tests run on the Visual Studio instance you need to test. They do not need Xunit or any other runner.
+
+1. Create or download the end-to-end test ZIP file and extract it to a directory. It is recommended you extract the files in the `artifacts` directory at the repo root.
+1. Run [SetupFunctionalTests.ps1](./SetupFunctionalTests.ps1). This step is executed once per machine.
+1. Start the Visual Studio instance you want to test. This can be a regular Visual Studio instance, with or without a VSIX that you want to test installed, but it can also be an [experimental Visual Studio instance](./../../docs/debugging.md#debugging-and-testing-nuget-in-visual-studio) you want to debug.
+1. Open the Package Manager Console and load the module from the unzipped end-to-end test package, [NuGet.Tests.psm1](./../../test/EndToEnd/NuGet.Tests.psm1), by running `Import-Module <NuGet.Tests.psm1 file path>`.
+1. Run a test:
+    - `Run-Test <TestName>` - The test name is the function name without a prefix `Test-`.
+    - `Run-Test <FileName>` - The file name is a filename from the generated zip file.
+    - `Run-Test` - Runs all tests the runner can discover based on the relative file location.
+
+## Debugging End-to-End tests
+
+1. Load the [experimental instance of Visual Studio](./../../docs/debugging.md#debugging-and-testing-nuget-in-visual-studio).
+1. Find the code in question, and set your breakpoints.
+1. Follow the [steps](#running-the-tests) for running the tests. Import the scripts in the experimental instance Package Manager Console.