[gtksourceview/win32-readme: 3/4] README.win32.md: Add info on ARM64 Windows builds

[Chun-wei Fan <fanchunwei src gnome org>]

commit d3604bd90ec2a688fe11ca87fcc1cecfcc14cce1
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Fri Jun 24 11:33:15 2022 +0800

    README.win32.md: Add info on ARM64 Windows builds

 README.win32.md | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)
---
diff --git a/README.win32.md b/README.win32.md
index 1d87da88..daba04c4 100644
--- a/README.win32.md
+++ b/README.win32.md
@@ -31,7 +31,10 @@ Meson command line.  For libxml2, if .pc files are not available, ensure that it
 import library can be found by ensuring your `%INCLUDE%` and `%LIB%` environment variables
 include these repective paths, and ensure that `cmake` is installed and in your `%PATH%`.
 For the introspection to complete successfully, you will also need to ensure that the DLLs
-can be found in the bindir entries of your .pc files or in your `%PATH%`.
+can be found in the bindir entries of your .pc files or in your `%PATH%`.
+
+ARM64 Windows builds are also supported provided that a valid cross compilation config file
+is set up and passed into the Meson command line using `--cross-file=...`.
 
 #### Building GtkSourceView