add youtube video links

documentation.html

@@ -152,11 +152,11 @@
                 <h2>User guide</h2>
                 <section id="user-guide">
                     <h3>Load patient</h3>
-                    <iframe width="560" height="315" src="https://www.youtube.com/embed/example_video_code" frameborder="0" allowfullscreen class="mb-4"></iframe>
+                    <iframe width="560" height="315" src="https://youtu.be/iXPMgLM7UYs" frameborder="0" allowfullscreen class="mb-4"></iframe>
                 </section>
                 <section id="edit-contours">
                     <h3>Edit contours</h3>
-                    <iframe width="560" height="315" src="https://www.youtube.com/embed/example_video_code" frameborder="0" allowfullscreen class="mb-4"></iframe>
+                    <iframe width="560" height="315" src="https://youtu.be/1YO3PYhbvzs" frameborder="0" allowfullscreen class="mb-4"></iframe>
                 </section>
             </section>
             <section id="folder-structure">