Add release notes and security notice for Tails 1.6.

wiki/src/inc/release_notes/1.6.mdwn

+## Upgrades and changes
+
+  - Upgrade *Tor Browser* to version 5.0.3 (based on
+    Firefox 38.3.0esr).
+  - Upgrade *I2P* to version 0.9.22 and enable its AppArmor profile.
+
+There are numerous other changes that might not be apparent in the daily
+operation of a typical user. Technical details of all the changes
+are listed in the [Changelog](https://git-tails.immerda.ch/tails/plain/debian/changelog).
+
+## Fixed problems
+
+  - Fix several issues related to *MAC address spoofing*:
+    * If MAC address spoofing fails for some network interface *and*
+      it cannot be disabled afterwards, networking should now be
+      completely disabled.
+    * If MAC address spoofing causes network issues (e.g. due to the
+      access point blocking all but whitelisted MAC addresses) a
+      notification should now be properly displayed.

wiki/src/news/version_1.6.mdwn

+[[!meta date="Tue Sep 22 12:34:56 2015"]]
+[[!meta title="Tails 1.6 is out"]]
+[[!tag announce]]
+
+Tails, The Amnesic Incognito Live System, version 1.6, is out.
+
+This release fixes [[numerous security
+issues|security/Numerous_security_holes_in_1.5.1]] and all users must
+[[upgrade|doc/first_steps/upgrade]] as soon as possible.
+
+[[!toc levels=1]]
+
+# Changes
+
+[[!inline pages="inc/release_notes/1.6" raw="yes"]]
+
+# Known issues
+
+See the current list of [[known issues|support/known_issues]].
+
+# Download or upgrade
+
+Go to the [[download]] page.
+
+# What's coming up?
+
+The next Tails release is [[scheduled|contribute/calendar]] for
+November 3.
+
+Have a look to our [[!tails_roadmap]] to see where we are heading to.
+
+Do you want to help? There are many ways [[**you** can
+contribute to Tails|contribute]], for
+example by [[donating|contribute/how/donate]]. If you want to help, come talk
+to us!

wiki/src/security/Numerous_security_holes_in_1.5.1.mdwn

+[[!meta date="Sun Sep 20 01:02:03 2015"]]
+[[!meta title="Numerous security holes in Tails 1.5.1"]]
+
+[[!tag security/fixed]]
+
+Several security holes that affect Tails 1.5.1 are now fixed in
+Tails 1.6.
+
+We **strongly** encourage you to [[upgrade to
+Tails 1.6|news/version_1.6]] as soon as possible.
+
+Details
+=======
+
+ - Tor Browser: MFSA:s not announced yet.
+ - bind9: [[!debsa2015 3350]]
+ - liblcms1: [[!cve CVE-2013-4276]]
+ - libldap-2.4-2: [[!debsa2015 3356]]
+ - libslp1: [[!debsa2015 3353]]
+ - ssl-cert: [[!debbug 773815]]