Add some findings about timescaledb

Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>

docs/datanommer_datagrepper/pg_timescaledb.rst

@@ -53,3 +53,12 @@ Finally, you can check that the extension was activated for your database:
 ::
     $ sudo -u postgres psql <database_name>
     \dx
+
+
+Findings
+--------
+
+After converting the `messages` table to use timescaledb, we've realized that
+timescaledb uses table partitioning as well.
+This leads to the same issue with the foreign key constraints that we have seen
+in the plain partitioning approach we took.