This works on most major DEs

1. Install xcape on your distro
2. Create file .config/autostart/xcape.desktop with contents

   [Desktop Entry]
   Type=Application
   Name=Shift to parenthesis mapping
   Exec=xcape -e "Shift_L=parenleft;Shift_R=parenright"
   X-GNOME-Autostart-enabled=true
   NoDisplay=false