wingrass: document GRASS_SH (how to switch from cmd to bash) (merge https://trac.osgeo.org/grass/changeset/68212 from trunk)

git-svn-id: https://svn.osgeo.org/grass/grass/branches/releasebranch_7_0@68213 15284696-431f-4ddb-bdfa-cd5b030d7da7

mswindows/osgeo4w/env.bat.tmpl

@@ -4,6 +4,10 @@ REM
 
 set GISBASE=%OSGEO4W_ROOT%\apps\grass\grass-@VERSION@
 
+REM Uncomment if you want to use Bash instead of Cmd
+REM Note that msys package must be also installed
+REM set GRASS_SH=%OSGEO4W_ROOT%\apps\msys\bin\sh.exe
+
 set GRASS_PYTHON=%OSGEO4W_ROOT%\bin\python.exe
 set PYTHONHOME=%OSGEO4W_ROOT%\apps\Python27