Update cheatsheets

tldr/linux/lxc-start

@@ -8,6 +8,18 @@ source: https://github.com/tldr-pages/tldr.git
 > Start a container.
 > More information: <https://linuxcontainers.org/lxc/getting-started/>.
 
+- Start the lxc service:
+
+`systemctl start lxc-net`
+
 - Start a container:
 
 `sudo lxc-start {{container_name}}`
+
+- Start a container in the foreground:
+
+`sudo lxc-start {{container_name}} {{[-F|--foreground]]}`
+
+- Exit out of a foreground container (run this in a separate terminal):
+
+`sudo lxc-stop {{container_name}}`