Update index.htm to include CORS issue text

Author: lost-hope

index.htm

@@ -76,6 +76,9 @@ <h2>Welcome to the WLED web installer!</h2>
       >
         <button class="btn" slot="activate">Install</button>
       </esp-web-install-button><br>
+<br> If you get download or fetching errors, or error code 403 when using the webinstaller, please try this <a href="https://lost-hope.github.io/WLED-WebInstaller/">alternative version.</a> <br>
+		It requires to use a browser plugin like "CORS unblock". Otherwise it would fail. 
+		
 </div>
 <br></brY><br>Powered by <a href="https://esphome.github.io/esp-web-tools/" target="_blank">ESP Web Tools</a><br>
 <br><a href="https://github.com/Aircoookie/WLED" target="_blank">GitHub</a>&emsp;<a href="https://kno.wled.ge" target="_blank">kno.wled.ge</a>
@@ -85,4 +88,4 @@ <h2>Welcome to the WLED web installer!</h2>
   src="script.js"
 ></script>
 </body>
-</html>
+</html>