flux-start(1): document --recovery

Problem: flux-start(1) does not document the --recovery option.

Add an entry in the option table, and an example.

doc/man1/flux-start.rst

@@ -96,6 +96,13 @@ OPTIONS
    ``per-broker``, each broker is placed in its own clique.
    Default: ``single``.
 
+**-r, --recovery**\ =\ *[STATEDIR]*
+   Start the rank 0 broker of an instance in recovery mode.  If *statedir*
+   is unspecified, ``/var/lib/flux`` is assumed and the system instance
+   configuration is sourced.  Any rc1 errors are ignored, broker peers are
+   not allowed to connect, and resources are offline during recovery.  An
+   initial program is started in which repairs can be made.
+
 VERBOSITY LEVELS
 ================
 
@@ -123,6 +130,18 @@ shell as the initial program:
 
    srun --pty -N8 flux start
 
+Start the system instance rank 0 broker in recovery mode:
+
+::
+
+   sudo -u flux flux start --recovery
+
+Start a non-system instance in recovery mode:
+
+::
+
+   flux start --recovery=/tmp/statedir
+
 
 RESOURCES
 =========

doc/test/spell.en.pws

@@ -666,3 +666,4 @@ sigpending
 chunksize
 taskmap
 multiline
+sudo