[libxmlplusplus/nmake-3-2] Update MSVC_NMake/README

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

commit e2c32093065026dd2b8ef076af619c56d17f0a49
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Fri Jun 12 15:54:15 2020 +0800

    Update MSVC_NMake/README
    
    Update instructions for building since we moved to using NMake
    Makefiles, and let people know that the same compiler version is
    required for building libxml++, glibmm and libsigc++.

 MSVC_NMake/README | 33 +++++++++++++++++++--------------
 1 file changed, 19 insertions(+), 14 deletions(-)
---
diff --git a/MSVC_NMake/README b/MSVC_NMake/README
index 4b5058a..d659eaa 100644
--- a/MSVC_NMake/README
+++ b/MSVC_NMake/README
@@ -1,14 +1,19 @@
-Building libxml++ with Visual Studio 2010
-
-* You will need Visual Studio 2010 (MSVC 10.0).  See the MSVC_Net2005/ folder if you want to build libxml++ 
using Visual Studio .NET 2005 (MSVC 8.0) or the MSVC_Net2008 folder if you want to build libxml++ using 
Visual Studio .NET 2008 (MSVC 9.0). Earlier versions of the compiler, including 6.0, 7.0 and 7.1 will not 
work.  
-* Install the latest Win32 GTK+ Development files from ftp://ftp.gnome.org/pub/GNOME/binaries/win32/gtk+/
-* Build libsigc++ 2.0.6 and glibmm from source
-* Add GTK+, libsigc++ and glibmm to the include and lib paths in Visual Studio. 
-* Load the MSVC_NMake/libxml++.sln solution. 
-* Build the entire solution.  Run the tests.
-
-Cedric Gustin
-01/26/2005
-
-Armin Burgmeier
-10/03/2010
+Building libxml++ with Visual Studio 2017 or later
+
+* You will need Visual Studio 2017 (MSVC 16.0) or later.  Unfortunately, due to a compiler that forbids using
+  `explicit` with `virtual` (and the likes), Visual Studio 2015 and earlier are not supported, even though
+  only C++-11 is required,
+* Install the latest Win32 GTK+ Development files from ftp://ftp.gnome.org/pub/GNOME/binaries/win32/gtk+/
+* Build libsigc++ 2.0.6 and glibmm from source, with the same compiler version.
+* Add GTK+, libsigc++ and glibmm to the include and lib paths in Visual Studio.
+* Run `nmake /f Makefile.vc CFG=[debug|release]` to buiild libxml++.  Run `nmake /f Makefile.vc` without the
+  `CFG=[debug|release] flag to see which options are supported by the NMake Makefiles
+
+Cedric Gustin
+01/26/2005
+
+Armin Burgmeier
+10/03/2010
+
+Chun-wei Fan
+06/12/2020