Explain why we ship Tor Browser 6.0.8-build1.

debian/changelog

 tails (2.9) UNRELEASED; urgency=medium
 
   * Security fixes
-    - Upgrade Tor Browser to 6.0.8 based on Firefox 45.6. (Closes:
-      #12028)
+    - Upgrade Tor Browser to 6.0.8 based on Firefox 45.6. If you pay
+      close attention you'll see that we import -build1 but there was
+      a -build2. The only change is Tor Button 1.9.5.13 which makes
+      some changes to the donation campaign banner in `about:tor`,
+      which we safely can skip. (Closes: #12028)
     - Upgrade Icedove to 45.5.1-1~deb8u1+tails1. (Closes: #12029)
 
   * Minor improvements