flux-config-kvs(5): add new man page

Problem: No documentation for the new [kvs] config options
exists.

Add man page.

doc/Makefile.am

@@ -292,7 +292,8 @@ MAN5_FILES_PRIMARY = \
 	man5/flux-config-resource.5 \
 	man5/flux-config-archive.5 \
 	man5/flux-config-job-manager.5 \
-	man5/flux-config-ingest.5 
+	man5/flux-config-ingest.5 \
+	man5/flux-config-kvs.5
 
 
 MAN7_FILES = $(MAN7_FILES_PRIMARY)

doc/man5/flux-config-kvs.rst

@@ -0,0 +1,46 @@
+==================
+flux-config-kvs(5)
+==================
+
+
+DESCRIPTION
+===========
+
+The Flux system instance **kvs** service provides the primary key value
+store (i.e. "the KVS") for a large number of Flux services.  For
+example, job eventlogs are stored in the KVS.
+
+The ``kvs`` table may contain the following keys:
+
+
+KEYS
+====
+
+sync
+   (optional) The period of time (in RFC 23 Flux Standard Duration
+   format) that the KVS will regularly checkpoint a reference to its
+   primary namespace.  The checkpoint is used to protect against data
+   loss in the event of a Flux broker crash.
+
+
+EXAMPLE
+=======
+
+::
+
+   [kvs]
+   sync = "30m"
+
+
+RESOURCES
+=========
+
+Flux: http://flux-framework.org
+
+RFC 23: Flux Standard Duration: https://flux-framework.readthedocs.io/projects/flux-rfc/en/latest/spec_23.html
+
+
+SEE ALSO
+========
+
+:man5:`flux-config`