README.md: add snippets to k3s examples to download sysext to /etc/ex…

…tensions/k3s.raw

README.md

@@ -287,18 +287,30 @@ variant: flatcar
 version: 1.0.0
 storage:
   links:
+  files:
+    # filename needs to be k3s.raw
+    - path: /etc/extensions/k3s.raw
+      contents:
+        source: https://github.com/flatcar/sysext-bakery/releases/download/latest/k3s-v1.29.2+k3s1-x86-64.raw
     - path: /etc/systemd/system/multi-user.target.wants/k3s.service
       target: /usr/local/lib/systemd/system/k3s.service
       overwrite: true
 ```
 
+Please note that this way you will not get automatic updates via
+`systemd-sysupdate`.
+
 For a k3s agent (worker node) you would use something like this snippet:
 
 ```yaml
 variant: flatcar
 version: 1.0.0
 storage:
   links:
+    # filename needs to be k3s.raw
+    - path: /etc/extensions/k3s.raw
+      contents:
+        source: https://github.com/flatcar/sysext-bakery/releases/download/latest/k3s-v1.29.2+k3s1-x86-64.raw
     - path: /etc/systemd/system/multi-user.target.wants/k3s-agent.service
       target: /usr/local/lib/systemd/system/k3s-agent.service
       overwrite: true