installer/portable: include the start script

It was pointed out by Orgad Shaneh that the `start` script is not part
of the end users' Git for Windows installation.

This script is part of the `filesystem` package. As that package
contains files we do not want to ship with Git for Windows, we pluck
just the `start` script out of it.

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

make-file-list.sh

@@ -56,6 +56,7 @@ mingw$BITNESS/etc/gitconfig
 etc/post-install/01-devices.post
 etc/post-install/03-mtab.post
 etc/post-install/06-windows-files.post
+usr/bin/start
 usr/bin/dash.exe
 usr/bin/rebase.exe
 usr/bin/rebaseall