Add shoutout for 2026 beta testing to help screen (#808)

Author: sciencewhiz

vscode-wpilib/resources/webviews/help.html

@@ -11,6 +11,15 @@ <h1>WPILib Help</h1>
 
     <p>Welcome to WPILib Help!</p>
 
+    <p>
+      Thank you for beta testing the 2026 WPILib. Please see the
+      <a href="https://docs.wpilib.org/en/latest/docs/beta/beta-getting-started/welcome.html"
+        >the beta test instructions</a
+      >
+      for the expectations for beta testing and provide your feedback at
+      <a href="https://github.com/wpilibsuite/2026Beta">https://github.com/wpilibsuite/2026Beta</a>.
+    </p>
+
     <p>
       To open this window again, open the Command Palette (F1 or View->Command Palette), and select
       <b>Open WPILib Help.</b>