[librsvg/update-msvc-doc: 3/4] win32/README.txt: Update instructions for building from GIT checkouts

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

commit b5d27309bc05aa8bd32d29b8ed062210975e28f6
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Fri Apr 29 23:46:05 2022 +0800

    win32/README.txt: Update instructions for building from GIT checkouts
    
    There is now support to prepare building directly from the GIT checkout without
    the need to manually copy and edit files.  Mention about such support.

 win32/README.txt | 17 ++++++++---------
 1 file changed, 8 insertions(+), 9 deletions(-)
---
diff --git a/win32/README.txt b/win32/README.txt
index 303d62b05..a0d44fa62 100644
--- a/win32/README.txt
+++ b/win32/README.txt
@@ -62,15 +62,14 @@ x86/x86-64 Windows 7+ or on Windows 10 ARM64.
 It is recommended that the dependent libraries are built with the same version
 of Visual Studio that is being used to build librsvg, as far as possible.
 
-If building from a git checkout is desired, you will need to open the following
-*.in files, and replace any items that are surrounded by the '@' characters,
-and save those files without the .in file extension:
-
-(open file)                           -> (save as file)
-===========                              ==============
-config-msvc.mak.in                    -> config-msvc.mak
-config.h.win32.in                     -> config.h.win32
-$(srcroot)\librsvg\rsvg-version.h.in  -> $(srcroot)\librsvg\rsvg-version.h
+If building from a git checkout is desired, you will need to run in this directory (not supported in an 
unpacked release tarball):
+
+nmake /f generate-msvc.mak generate-nmake-files
+
+You may need to pass in PYTHON=<path_to_python_interpreter> in the
+NMake command line above if your Python interpreter is not in your
+%PATH%.  Run `nmake /f generate-msvc.mak remove-generated-nmake-files`
+to remove any generated files
 
 From this directory in a Visual Studio command prompt, run the following: