add changes file for bug 5283

I called it a bugfix on 0.2.0.10-alpha, since git commit e5885deab is
where we introduced anonymized begin_dir connections.

changes/bug5283

@@ -0,0 +1,6 @@
+  o Major bugfixes:
+    - Fix an edge case where if we fetch or publish a hidden service
+      descriptor, we might build a 4-hop circuit and then use that circuit
+      for exiting afterwards -- even if the new last hop doesn't obey our
+      ExitNodes config option. Fixes bug 5283; bugfix on 0.2.0.10-alpha.
+