Clarify custom CNI is not covered by k0s reset

Signed-off-by: Juan-Luis de Sousa-Valadas Castaño <[email protected]>

docs/reset.md

@@ -21,7 +21,7 @@ following:
   network interfaces or iptables rules set up specifically for cluster
   communication. This is done on a best effort basis. It's recommended that you
   reboot the host after a reset to ensure that there are no k0s remnants in the
-  host's network configuration.
+  host's network configuration. Custom CNI plugins are not cleaned up.
 * Registration with the host's init system: Reverts the registration done by
   `k0s install`. After a reset, k0s won't be automatically started when the host
   boots.