[PATCH website] downloads: add link to PPA for ubuntu/debian

[heatherboo]

# HG changeset patch
# User heatherboo <heather.j.booker at gmail.com>
# Date 1488054963 28800
#      Sat Feb 25 12:36:03 2017 -0800
# Node ID b91f88bda2404c91722a62a2eb9afc63867a172b
# Parent  f8cee73d5cf0e9b4d46859c949ed0e23d65dd38c
downloads: add link to PPA for ubuntu/debian

diff --git a/templates/downloads/index.html b/templates/downloads/index.html
--- a/templates/downloads/index.html
+++ b/templates/downloads/index.html
@@ -114,7 +114,9 @@
     GUI the most. It integrates Mercurial directly into your explorer.</p>
 
     <p>Packages for common Linux, BSD and Solaris distributions can be
-    installed from the system specific repositories</p>
+    installed from the system specific repositories:</p>
+    <p>(Debian/Ubuntu: If you need a more recent version than what is available through apt-get, you can <a href="https://launchpad.net/~mercurial-ppa/+archive/ubuntu/releases">try the PPA</a>.)
+    </p>
     <p>
 <pre>
 # Debian/Ubuntu