Update Windows build instruction for 14393 SDK

docs/windows_build_instructions.md

Index: docs/windows_build_instructions.md
diff --git a/docs/windows_build_instructions.md b/docs/windows_build_instructions.md
index f13f63d1c60b96c234a0de99a50a0d64a973ad0f..fc9664d061739350e530e59baadc4d68967619d2 100644
--- a/docs/windows_build_instructions.md
+++ b/docs/windows_build_instructions.md
@@ -34,12 +34,13 @@ and select:
 - Universal Windows Apps Development Tools > Tools (1.4.1) and Windows 10 SDK
   (10.0.14393)
 
-You must have the 14393 SDK installed or else you will hit compile errors such
-as undefined or redefined macros.
+You must have the 14393 Windows SDK installed. It is okay to have multiple
+SDK versions installed as long as 14393 is one of them. The installer can be
+found in the [Windows SDK archive](https://developer.microsoft.com/en-us/windows/downloads/sdk-archive).

[scottmg, 2017/04/26 23:06:30]

Maybe say 15063 is broken? Up to you.

[brucedawson, 2017/04/26 23:23:56]

Done.

 
-Install the Windows SDK 10, and choose Debugging Tools For Windows when you
-install this in order to get windbg and cdb. The latter is required for the
-build to succeed as some tests use it for symbolizing crash dumps.
+When installing the 14393 Windows SDK choose Debugging Tools For Windows in order
+to get windbg and cdb. The latter is required for the build to succeed as some
+tests use it for symbolizing crash dumps.
 
 ## Install `depot_tools`