[gtk-web/vcpkg-warn] Add a warning about vcpkg

[Emmanuele Bassi <ebassi src gnome org>]

commit 37dabe442d6ad08dfb70e34c673b974b36de5580
Author: Emmanuele Bassi <ebassi gnome org>
Date:   Thu Jul 4 17:10:05 2019 +0100

    Add a warning about vcpkg
    
    We don't support it, so we can't fix it.

 download/windows.php | 6 ++++++
 1 file changed, 6 insertions(+)
---
diff --git a/download/windows.php b/download/windows.php
index 52ef466..50aabba 100644
--- a/download/windows.php
+++ b/download/windows.php
@@ -37,6 +37,12 @@ versions of GLib and GTK.</p>
 
 <h2><a name="Vcpkg">Using GTK from vcpkg packages</a></h2>
 
+<p><b>WARNING</b>: The vcpkg packaging is not maintained by the GTK team,
+and it uses a different build system than the one used by GTK. If
+something breaks when building GTK or its dependencies using vcpkg, make
+sure to open an issue in the <a href="https://github.com/Microsoft/vcpkg/issues";
+class="external">vcpkg issue tracker</a>, instead of the GTK one.</p>
+
 <h3>Installation</h3>
 
 <p>The GTK library, as well as all pre-requisites and many language