[gobject-introspection] MSVC.README.rst: Be more clear on Python requirements

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

commit 897b1ce0fa3b40a04d252178e07a3514f31b8c15
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Mon Aug 20 17:45:48 2018 +0800

    MSVC.README.rst: Be more clear on Python requirements
    
    Let people know the common pitfalls when building and using the Python
    scripts when building, to avoid confusions on the Python installation
    that is used to run the Python scripts.

 MSVC.README.rst | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)
---
diff --git a/MSVC.README.rst b/MSVC.README.rst
index a666f59d..06cdf75f 100644
--- a/MSVC.README.rst
+++ b/MSVC.README.rst
@@ -42,11 +42,14 @@ You will need the following, in addition to your Visual Studio installation:
   as they run on your system.
 
 Set PATH to contain your Python-3.4.x+ interpreter, Ninja build tool (if needed) and
-winflex/flex and Bison executables towards its end.
-
-Note that if you plan to use g-ir-scanner for other packages built using Meson, you
-need to use the same Python release series (3.4, 3.5...) for running Meson there as
-well.
+winflex/flex and Bison executables towards its end.  Please note that if using Python
+2.7.x (such as with the case of building with Visual Studio 2008), the PATH variable
+needs to contain the native Windows Python 2.7.x installation path as well, before
+the path where the Flex and Bison executables are, if using the Flex and Bison
+executables from MSYS2 or Cygwin, as the copy of the Python interpreter from MSYS2
+and Cygwin will likely conflict with the installation of the native Windows Python
+2.7.x.  Please note that building against MSYS2 or Cygwin Python with Visual Studio
+builds is not (and will likely never be) supported.
 
 Open a Visual Studio command prompt and create an empty build directory (which needs
 to be on the same drive as the G-I sources).  In that directory, run the following::
@@ -60,6 +63,7 @@ DLL filename for Cairo-GObject that is built with MinGW/mingw-w64.
 The -Dpython is likely necessary when using multiple Python installations on the
 system and is necessary when building with Visual Studio 2008~2013 when building
 with later versions of Meson (which requires Python 3.5+), due to CRT differences.
+Note that for this setting, Python-2.7.x or Python-3.4.x or later is supported.
 
 When Meson completes configuring and generating the build files, proceed building
 using Ninja or the generated Visual Studio projects.