Add "Generate random number" on bottom of patcher

patcher/index.html

@@ -59,6 +59,11 @@
       <a href="#" onclick="defines()">download configkeys.h</a>.
     </p>
 
+    <p>
+      <a href="#" id="rnd">Generate random number</a>
+      <span id="rnd-res"></span>
+    </p>
+
 
   <footer>
     <a href="https://makecode.com/privacy" target="_blank" rel="noopener">Privacy &amp; Cookies</a>

patcher/web.js

@@ -5,10 +5,18 @@ function savePatch(ev) {
     localStorage["UF2_PATCH"] = text.value
 }
 
+function genRnd() {
+    let vals = new Uint32Array(1)
+    window.crypto.getRandomValues(vals)
+    document.getElementById("rnd-res").textContent = "Random number: 0x" + 
+        ("000000000" + vals[0].toString(16)).slice(-8)
+}
+
 function restorePatch() {
     let text = document.getElementById("patch")
     text.value = localStorage["UF2_PATCH"] || ""
     document.getElementById("apply").onclick = applyPatch
+    document.getElementById("rnd").onclick = genRnd
 }
 
 function download(buf, name) {