doc: add a little note about shared ns + LSMs
doc: add a little note about shared ns + LSMs

We should add a little not about the race in the previous patch.

Signed-off-by: Tycho Andersen <6b523322678240882acbb4da5312a12d8cd0082d@tycho.ws>

hallyn/lxc,hallyn/lxc,ss1h2a3tw/lxc,hallyn/lxc,ss1h2a3tw/lxc,ss1h2a3tw/lxc