add extra explanation for device targets

static/build.html

@@ -116,6 +116,15 @@
                 <li>aosp_sargo (Pixel 3a)</li>
             </ul>
 
+            <p>These are all fully supported production-ready targets supporting all the baseline
+            security features and receiving full monthly security updates covering all firmware,
+            kernel drivers, driver libraries / services and other device-specific code. A fully
+            signed user build for these devices is a proper GrapheneOS release. Newer generation
+            devices have stronger hardware / firmware security and hardware-based OS security
+            features and are better development devices for that reason. It's not possible to work
+            on everything via past generation devices. The best development devices are the Pixel
+            3, Pixel 3 XL, Pixel 3a and Pixel 3a XL.</p>
+
             <p>Generic targets:</p>
 
             <ul>