org-protocol: Fix missing '+' in js snippet

* org-protocol (org-protocol-capture): Add missing plus-sign to
javascript snippet to allow readers of the doc string to use example
snippet with minimal edits.

TINYCHANGE

lisp/org-protocol.el

@@ -462,7 +462,7 @@ This function detects an URL, title and optional text, separated
 by `/'.  The location for a browser's bookmark looks like this:
 
   javascript:location.href = \\='org-protocol://capture?url=\\='+ \\
-        encodeURIComponent(location.href) + \\='&title=\\=' \\
+        encodeURIComponent(location.href) + \\='&title=\\=' + \\
         encodeURIComponent(document.title) + \\='&body=\\=' + \\
         encodeURIComponent(window.getSelection())