new script: sane-private-lock

this is handy esp for `servo`, where i don't want my keys to be
accessible after i logout.

longterm, i suppose i could run this automatically on session close
(pam-umount or something i think exists for that?)

pkgs/sane-scripts/src/sane-private-lock

@@ -0,0 +1,3 @@
+#!/usr/bin/env bash
+
+sudo umount /home/colin/private