Docs for Snap WRITABLE_PATH.

Thanks to xet7 !

snap-src/bin/wekan-help

@@ -15,6 +15,12 @@ echo -e "\t$ snap set $SNAP_NAME debug='true'"
 echo -e "\t-Disable the Debug of Wekan:"
 echo -e "\t$ snap unset $SNAP_NAME debug"
 echo -e "\n"
+echo -e "Writable path. Snap can not write outside of /var/snap/wekan/common sandbox directory."
+echo -e "Default:"
+echo -e "\t$ snap set $SNAP_NAME writable-path='\$SNAP_COMMON\uploads'"
+echo -e "\t-To set different path, usually not needed:"
+echo -e "\t$ snap set $SNAP_NAME writable-path='\$SNAP_COMMON\uploads2'"
+echo -e "\n"
 echo -e "Mongo log destimation: devnull/snapcommon/syslog. Default: 'devnull'"
 echo -e "To set different mongo log destination of Wekan:"
 echo -e "\t$ snap set $SNAP_NAME mongo-log-destination='snapcommon'"