Fix misleading comment

Related to https://github.com/spantaleev/matrix-docker-ansible-deploy/pull/2086

roles/matrix-conduit/defaults/main.yml

@@ -38,7 +38,7 @@ matrix_conduit_max_request_size: 20_000_000
 
 # Maximum number of open files for Conduit's embedded RocksDB database
 # See https://github.com/facebook/rocksdb/wiki/RocksDB-Tuning-Guide#tuning-other-options
-# If not specified, Conduit defaults to a relatively low value of 20
+# By default, Conduit uses a relatively low value of 20.
 matrix_conduit_rocksdb_max_open_files: 64
 
 # Enables registration. If set to false, no users can register on this server.