Update index.html

Renamed user to key ID to reflect the change in the API

Author: rexgnu

index.html

@@ -45,7 +45,7 @@ <h1 id="test">Settle API PKCS#1 1.5 signature generator</h1>
     </div>
 
     <div class="pure-control-group">
-      <label for="api_user">API User</label>
+      <label for="api_user">API key ID</label>
       <input type="text" name="api_user" id="api_user"></input>
     </div>
 
@@ -86,4 +86,4 @@ <h1 id="test">Settle API PKCS#1 1.5 signature generator</h1>
   <script src="index.js"></script>
 </body>
 
-</html>
+</html>