Document changes and release 2.1.7pureos0

debian/changelog

+python-apt (2.1.7pureos0) byzantium; urgency=medium
+
+  * Merge with Debian unstable, remaining changes:
+    - Add PureOS template and mirror lists
+
+ -- Guido Günther <agx@sigxcpu.org>  Tue, 02 Feb 2021 17:19:42 +0100
+
 python-apt (2.1.7) unstable; urgency=medium
 
   * SECURITY UPDATE: various memory and file descriptor leaks (LP: #1899193)