DOCS-11233 journal commit interval (#680) (#684)

* DOCS-11233-journal-commit-interval

* DOCS-11233-journal-commit-interval

* DOCS-11233-journal-commit-interval

Co-authored-by: jason-price-mongodb <[email protected]>

Co-authored-by: jason-price-mongodb <[email protected]>

Author: jason-price-mongodb

source/reference/write-concern.txt

@@ -217,6 +217,9 @@ the write operation has been written to the :doc:`on-disk journal
      configuration setting determines the behavior. See
      :ref:`wc-ack-behavior` for details.
 
+   - A write concern that includes or implies ``j: true`` causes an
+     immediate journal synchronization. See :ref:`journal-process`.
+
 .. _wc-wtimeout:
 
 ``wtimeout``