Add timestamp auto link doc

client/src/app/+videos/+video-edit/shared/video-edit.component.html

@@ -45,9 +45,11 @@
 
               <my-help helpType="markdownText">
                 <ng-template ptTemplate="preHtml">
-                  <ng-container i18n>
-                    Video descriptions are truncated by default and require manual action to expand them.
-                  </ng-container>
+                  <ng-container i18n>Video descriptions are truncated by default and require manual action to expand them.</ng-container>
+
+                  <br />
+
+                  <ng-container i18n>A timestamp (<i>00:05</i> for example) is automatically converted into a link to a part of the video.</ng-container>
                 </ng-template>
               </my-help>