debian: add some hints about upstream changes.

debian/changelog

@@ -1,20 +1,26 @@
-notmuch (0.26-1) UNRELEASED; urgency=medium
+notmuch (0.26-1) unstable; urgency=medium
 
-  * New upstream release
+  [ Daniel Kahn Gillmor ]
   * build against python3-sphinx instead of python-sphinx
   * d/changelog: strip trailing whitespace
   * move to debhelper 10
   * Standards-Version: bump to 4.1.3 (drop priority: extra
     from transitional packages)
+
+  [ David Bremner ]
+  * New upstream release (see /usr/share/doc/notmuch/NEWS.gz)
+    - new command 'notmuch reindex'
+    - optional indexing of encrypted emails.
+    - indexing of files with duplicate message-id
   * update symbols
 
- -- Daniel Kahn Gillmor <dkg@fifthhorseman.net>  Sun, 07 Jan 2018 09:36:24 -0500
+ -- David Bremner <bremner@debian.org>  Tue, 09 Jan 2018 07:13:21 -0400
 
 notmuch (0.26~rc2-1) experimental; urgency=medium
 
   * Third upstream release candidate
 
- -- David Bremner <bremner@debian.org>  Sat, 06 Jan 2018 09:39:17 -0400
+ -- David Bremner <bremner@debian.org>  Tue, 09 Jan 2018 07:13:11 -0400
 
 notmuch (0.26~rc1-1) experimental; urgency=medium