Add SD URL

Author: dspinellis

README.md

@@ -532,6 +532,6 @@ e6a95c9 - New issue entered from the command line
   code review system for Git repos based again on Git.
 * [Fossil](http://fossil-scm.org/) is a distributed version control software that also supports issue tracking and a wiki. It runs as a single executable.
 * [Perceval](https://github.com/chaoss/grimoirelab-perceval) can download issues from a variety of systems, including GitHub and GitLab.
-* [SD (Simple Defects)], a (now defunct?) distributed bug tracking system based on a distributed database. It can import/export from/to foreign ticketing systems.
+* [SD (Simple Defects)](https://syncwith.us/sd/), an (unmaintained) distributed bug tracking system based on a distributed database. It can import/export from/to foreign ticketing systems.
 
 More historical references can be found in [this old LWN article on distributed bug tracking](https://lwn.net/Articles/281849/).