added download button to watch page

html/watch.html

@@ -11,6 +11,7 @@
     <p id="copyStatus"></p>
     <input class="form-control" type="text" value="{serverURL}/video\?v\={videoURL}\&api\={api}" id="directLink">
     <button class="btn btn-secondary align-content-center" onclick="copyVideoPath()">Copy Direct Link</button>
+    <a class="btn btn-secondary align-content-center" href="/video?v={videoURL}" download="{videoURL}">Download</a>
 </div>
 
 <script>