doc: knotc: describe the force option for zone-flush

diff --git a/doc/man_knotc.rst b/doc/man_knotc.rst
index 20ca8a3dd7d4b89be8704d783ba58848b6c59d3f..d44d6c067a6b3fc8c41721cff5f62d8b3ab8da48 100644 (file)
--- a/doc/man_knotc.rst
+++ b/doc/man_knotc.rst
@@ -128,9 +128,10 @@ Actions
   offline. (#)
 
 **zone-flush** [*zone*...] [**+outdir** *directory*]
-  Trigger a zone journal flush to the configured zone file. If an output
-  directory is specified, the current zone is immediately dumped (in the
-  blocking mode) to a zone file in the specified directory. See
+  Trigger a zone journal flush to the configured zone file. If zonefile
+  synchronization is disabled, the force option must be used.
+  If an output directory is specified, the current zone is immediately
+  dumped (in the blocking mode) to a zone file in the specified directory. See
   :ref:`Notes<notes>` below about the directory permissions. (#)
 
 **zone-backup** [*zone*...] **+backupdir** *directory* [*filter*...]