Add FAQ why Tails includes old versions of software

wiki/src/support/faq.mdwn

@@ -512,6 +512,13 @@ If there is no known workaround for the issue you are experiencing, you might
 want to [[make a bug report|doc/first_steps/bug_reporting]] to let us know
 about the issue.
 
+<h2 id="old-software">Why does Tails include old versions of software?</h2>
+
+Tails includes the software versions that are found in
+[Debian stable](https://wiki.debian.org/DebianStable). Even though the
+software versions might be old, they receive security fixes through the
+[Debian security team](https://wiki.debian.org/Teams/Security).
+
 <h2 id="compromised-system">Is it safe to use Tails on a compromised system?</h2>
 
 Tails runs independently from the operating system installed on the computer.