clarified lxc / lxd difference

README.md

@@ -499,10 +499,12 @@ riverctl float-filter-add title 'Firefox — Sharing Indicator'
 
 ## Development (containers)
 
-### Unprivileged LXC with routing
+### Unprivileged LXC (ran without privileges on host), with routing
 
 (based partially on https://linuxcontainers.org/lxc/getting-started and https://wiki.alpinelinux.org/wiki/LXC)
 
+**Note that docker won't work inside this container**, you'll need to create container using privileged LXD, as described in the next section (see https://discuss.linuxcontainers.org/t/lxc-on-alpine-host-sys-fs-cgroup-is-not-mounted-into-unprivileged-alpine-guest/15026/1 for more details on why this doesn't work).
+
 #### Networking (host)
 
 (assuming that your internet-connected interface is eth0,
@@ -628,7 +630,7 @@ Now exit root shell (just with `exit`), and try `lxc-console -n CONTAINERNAME`.
 You should be able to log in using the new username and password.
 (To exit lxc console, use Ctrl+A, Q).
 
-### Alternatively: unprivileged LXC using LXD
+### Alternatively: unprivileged LXC using LXD (ran as privileged service on host)
 
 #### Security notes