Minor format fix in 1984/mullender/README.md

And I forgot to mention in the previous commit that typo changes were
made and additional formatting too. I added some links that seemed
relevant. Due to the historical significance of the entry I had added
quite a few but few entries have this and I likely won't do it for any
additional entries as it takes too much time. Nevertheless to be
consistent with the rest of the file I did this as well.

1984/mullender/README.md

@@ -3,6 +3,7 @@
 Sjoerd Mullender<br>
 <https://github.com/sjoerdmullender><br>
 <br>
+
 Robbert van Renesse