Update README.md

Update README.md to be more concise about the environment variables.

Author: compnerd

README.md

@@ -28,48 +28,13 @@ ninja -C build SwiftWin32 UICatalog
 %CD%\build\bin\UICatalog.exe
 ```
 
-Following environment variables should be set/adjusted before run the above commands (the shown paths assume that you use compiler from the official swift installers from [swift.org](https://www.swift.org/download/)).
-
-- Visual Studio compiler toolchain
-
-  The CMake commands use the `mt` tool which requires a Visual Studio compiler environment (Build Tools should be fine too).
-  e.g. if you have Visual Studio 2019 installed you can create a command prompt by click on `x64 Native Tools Command Prompt for VS2019` from the Visual Studio 2019 installation in the Windows Start Menu.
-  
-  Newer versions of Visual Studio or the corresponding Build Tools should be fine too.
-
-  Another way of activating a Visual Studio environment is the tool [vswhere](https://github.com/microsoft/vswhere).
-
-- `SDKROOT`
-
-  This should be the path to the Windows Platform SDK from the Swift library. This should be already set by the official swift installer. If not set the env var.
-
-  \>= 5.10 `SDKROOT` needs to be `%LocalAppData%\Programs\Swift\Platforms\Windows.platform\Developer\SDKs\Windows.sdk`
-
-  < 5.10 `SDKROOT` needs to be `%SystemDrive%\Library\Developer\Platforms\Windows.platform\Developer\SDKs\Windows.sdk`
-
-  Examples for < 5.10:
-
-  Command Prompt: `set SDKROOT=%SystemDrive%\Library\Developer\Platforms\Windows.platform\Developer\SDKs\Windows.sdk`
-
-  PowerShell: `$env:SDKROOT="%SystemDrive%\Library\Developer\Platforms\Windows.platform\Developer\SDKs\Windows.sdk"`
-
-- `Path`
-
-  The `Path` environment variables needs to be extended to allow the Swift compiler to be found.
-  This is only required when this is not already the case.
-  When you type `where swiftc` (`(Get-Command swiftc).Path` for PowerShell) and see no path to `swiftc` the following command is required.
-
-  \>= 5.10 the `Path` needs to extended with `%LocalAppData%\Programs\Swift\Runtimes\5.9.0\usr\bin;%LocalAppData%\Programs\Swift\Toolchains\5.9.0+Asserts\usr\bin`
-
-  < 5.10 the `Path` needs to be extended with `%SystemDrive%\Library\Developer\Toolchains\unknown-Asserts-development.xctoolchain\usr\bin`
-
-  Examples for < 5.10:
-
-  Command Prompt: `set Path=%SystemDrive%\Library\Developer\Toolchains\unknown-Asserts-development.xctoolchain\usr\bin;%Path%`
-
-  PowerShell: `$env:Path="%SystemDrive%\Library\Developer\Toolchains\unknown-Asserts-development.xctoolchain\usr\bin;$env:Path"`
+<details>
+  <summary>Required Environment Variables</summary>
 
+  The CMake build will automatically perform the application manifest merging via the `mt` tool, which is part of the Visual Studio build tools.  Ensure that you run the build under the `x64 Native Tools Command Prompt for VS2019` (or the appropriate shell for the version of Visual Studio).
 
+  The Swift installer will also add environment variables, ensure that you have restarted the terminal emulator after installing the toolchain to pick up the required environment variables.
+</details>
 
 ### Swift Package Manager