changes: Add changes file for ticket 40833

Signed-off-by: David Goulet <dgoulet@torproject.org>

changes/ticket40833

+  o Major bugfixes (proof of work, onion service, hashx):
+    - Fix a very rare buffer overflow in hashx, specific to the dynamic compiler
+      on aarch64 platforms. Fixes bug 40833; bugfix on 0.4.8.2-alpha.