[glibmm/glibmm-2-62] README.win32: Mention that XML::Parser is required for builds from GIT

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

commit 7bee9a88d6dae68e9a1c3a2978acc6c028d35473
Author: Chun-wei Fan <fanchunwei src gnome org>
Date:   Wed Feb 26 11:56:22 2020 +0800

    README.win32: Mention that XML::Parser is required for builds from GIT
    
    The gmmproc PERL script actually requires the XML::Parser PERL module to be
    installed for the PERL interpreter.

 README.win32 | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)
---
diff --git a/README.win32 b/README.win32
index 45b723bd..cff86d10 100644
--- a/README.win32
+++ b/README.win32
@@ -72,7 +72,8 @@ with a few manual steps required, namely to:
  m4.exe and sh.exe.  You should also have a PERL for Windows installation
  as well, and your PATH should contain the paths to your PERL interpreter
  and the bin\ directory of your Cygwin or MSYS/MSYS64 installation, and
- it is recommended that these paths are towards the end of your PATH.
+ it is recommended that these paths are towards the end of your PATH.  You need
+ to install the XML::Parser PERL module as well, which requires libexpat.
 
 -Make a new copy of the entire source tree to some location, where the build
  is to be done; then: