Merge pull request #861 from coderefinery/chat_digest

add chat digest to newsletter page

content/about/newsletter.md

@@ -7,4 +7,7 @@ If you would like to receive our newsletter, please subscribe here:
 
 Expected frequency: 1 email every month or two.
 
+If you want to get **weekly** updates about what is happening in our chat, please subscribe to our "chat summary":
+<https://postit.csc.fi/sympa/subscribe/coderefinery-team>
+
 The service is hosted by CSC - IT Center for Science, Finland.