added raspberry installation hint (#2379)

Signed-off-by: Jordi Prats <jordi.prats@gmail.com>

install.sh

@@ -848,6 +848,11 @@ openrc_start() {
 
 # --- startup systemd or openrc service ---
 service_enable_and_start() {
+    if [ -f "/proc/cgroups" ] && [ "$(grep memory /proc/cgroups | while read -r n n n enabled; do echo $enabled; done)" -eq 0 ];
+    then
+        info 'Failed to find memory cgroup, you may need to add "cgroup_memory=1 cgroup_enable=memory" to your linux cmdline (/boot/cmdline.txt on a Raspberry Pi)'
+    fi
+
     [ "${INSTALL_K3S_SKIP_ENABLE}" = true ] && return
 
     [ "${HAS_SYSTEMD}" = true ] && systemd_enable