Add changes file for 17776

changes/bug17776

@@ -0,0 +1,6 @@
+  o Minor bugfixes (tests):
+    - Fix buffer over-reads in the directory tests. Fixes bug 17776; not in any
+      released version of Tor.
+    - Fix buffer over-reads in the rendcache tests. Fixes bug 17776; not in any
+      released version of Tor.
+