2014-02-09: readme: link to Mercurial.

readme: link to Mercurial.

diff --git a/README.txt b/README.txt
--- a/README.txt
+++ b/README.txt
@@ -15,10 +15,12 @@ information as hg serve and full solutio
 gitorious (naturally without the interactivity, but you can always
 clone the repo to interact).
 
-Thanks to the static http support of Mercurial, the clone and browse
+Thanks to the static http support of [Mercurial][], the clone and browse
 URLs are the same, so you can look at the site with your webbrowser or
 clone the repository with Mercurial using the same URL.
 
+[Mercurial]: http://mercurial.selenic.com "Fast and easy-to-use, free distributed version control system."
+
 The fork detection allows tieing multiple platforms together: It
 tracks repositories from any source for which Mercurial can calculate
 incoming and outgoing changes. And since the bugtracking happens via