Bookmark: Add 'via' link to the newsletter.

Change-Id: Ib969841b904dd5d9b8bcb4c1268892ee4d19f552
diff --git a/src/main/resources/templates/NewsletterSender/newsletter.txt b/src/main/resources/templates/NewsletterSender/newsletter.txt
index f70673e..4e2f395 100644
--- a/src/main/resources/templates/NewsletterSender/newsletter.txt
+++ b/src/main/resources/templates/NewsletterSender/newsletter.txt
@@ -19,6 +19,9 @@
 
 {#for post in bookmarks}
 * {post.date.humanDate}  <https://matthias.benkard.de/posts/{post.id}>
+{#if post.via}
+* Via: <{post.via}>
+{/if}
 * {post.title}
 * <{post.uri}>