about.rst: Fix comment.

I had put it in markdown syntax instead of rst...

Author: jordibc

doc/about.rst

@@ -54,7 +54,7 @@ Highlighted Tools Using ETE
 Related Links and Resources
 ---------------------------
 
-[//]: # (TODO: Clean up, since most are outdated and refer to ete3)
+.. TODO: Clean up, since most are outdated and refer to ete3.
 
 - `A brief introduction to ETE
   <https://www.youtube.com/watch?v=7yfMwmaptf0&index=64&list=PLYx7XA2nY5Gcpabmu61kKcToLz0FapmHu>`_