docs: Add "draft mode" notice to SECURITY.md

I just realized that this project now ha a SECURITY.md file. Never heard
of it before, but I love the idea and obviously have to get informed
about how this thing works. Hopefully there is some kind of automation
on GitHubs side for it?!

SECURITY.md

@@ -2,13 +2,15 @@
 
 ## Supported Versions
 
+Warning: Still draft mode!
+
 Use this section to tell people about which versions of your project are
 currently being supported with security updates.
 
 | Version | Supported          |
 | ------- | ------------------ |
-| 1.1.x   | :white_check_mark: |
-| 1.0.x   | :x:                |
+| 3.3.x   | :white_check_mark: |
+| 4.0.x   | :x:                |
 
 ## Reporting a Vulnerability