Adding bookmarklet option

resubmitting @gabrielgrant's [change request](dwhly-proj#80), but applied to the new version of index.html as per @genuineBuildMonkey's [comment](dwhly-proj#80 (comment))

Author: volt4ire

droppdf/apps/_templates/index.html

@@ -75,6 +75,9 @@
                     <br> <a href="/privacy/">Privacy Policy</a>.
                     </p>
 
+                    <p>To easily open YouTube videos for annotation, use the bookmarklet. Drag this link to the bookmarks bar, or right-click/control-click to bookmark the link:
+                    <a href='javascript:const dropdocBaseURL="https://docdrop.org/video",url=new URL(location.href);switch(url.host){case"youtu.be":location.href=`${dropdocBaseURL}${url.pathname}`;break;case"m.youtube.com":case"www.youtube.com":location.href=`${dropdocBaseURL}/${url.searchParams.get("v")}`;break;default:alert("Not a recognized Youtube URL")}'>DropDoc Bookmarklet</a>
+                    </p>
 
                     <!--<p>Scanned PDFs will be OCR’d<br/>(please ensure text is horizontal).</p>-->