readme: add ARM64 info to MSVC setup instructions

Since ARM64 build dependencies are not included in the "Desktop
development with C++" workload of Visual Studio 2017, this change adds
a note explaining what additional components are required to build
native modules for the new Windows platform.

PR-URL: #1655
Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: João Reis <reis@janeasystems.com>

README.md

@@ -55,6 +55,8 @@ Install tools and configuration manually:
 
    If the above steps didn't work for you, please visit [Microsoft's Node.js Guidelines for Windows](https://github.com/Microsoft/nodejs-guidelines/blob/master/windows-environment.md#compiling-native-addon-modules) for additional tips.
 
+   To target native ARM64 Node.js on Windows 10 on ARM, add the components "Visual C++ compilers and libraries for ARM64" and "Visual C++ ATL for ARM64".
+
 ### Configuring Python Dependency
 
 If you have multiple Python versions installed, you can identify which Python