Add additional explanation

Author: patrick96

native-image/wasm-javac/web/index.html

@@ -10,12 +10,21 @@
         <title>Javac on WebAssembly</title>
         <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
         <style type="text/css">
+            body {
+                font-family: Arial, Helvetica, sans-serif;
+                color: #ffffff;
+            }
+
             #content {
                 margin: 0 auto;
                 width: 900px;
                 padding-top: 40px;
             }
 
+            a {
+                color: #ffffff;
+            }
+
             #source {
                 box-shadow: 0px 4px 6px #1f9ddcb8;
                 &[contenteditable="false"] {
@@ -153,6 +162,8 @@
         </div>
         <div class="gen-back">
             <div id="content">
+                <span>This demo can turn Java source code into JVM bytecode, which you can then download or disassemble. For this, the demo uses the Java compiler (javac) on WebAssembly generated by GraalVM. It was shown as part of <a href="https://2025.wasm.io/sessions/the-future-of-write-once-run-anywhere-from-java-to-webassembly/" target="_blank">this talk</a> at Wasm I/O 2025.<br>
+                Note: This version of the demo has some rough edges, but we might improve it over time. Currently, the content of this text box will be written into a <code>HelloWasm.java</code> file. A valid program needs to use <code>public class HelloWasm</code> or only declare non-public classes.</span>
                 <pre id="source" contenteditable="false" spellcheck="false">
   public class HelloWasm {
       public static void main(String[] args) {