add slapos-build-installer.bat

windows/scripts/slapos-build-installer.bat

+@ECHO OFF
+SETLOCAL
+
+SET CYGWINHOME=%~dp0
+SET CYGWINROOT="%~dp0cygwin"
+
+CMD.EXE /C %CYGWINROOT%\bin\bash --login /slapos-build-installer
+
+ENDLOCAL
+EXIT 0