cow: Document config parameters
commit680960977425623c0449505e1b3def153bb1cf02
authorEric Blake <eblake@redhat.com>
Wed, 31 Jul 2019 20:36:56 +0000 (31 15:36 -0500)
committerEric Blake <eblake@redhat.com>
Wed, 31 Jul 2019 20:44:33 +0000 (31 15:44 -0500)
tree24f446ab4ca99b919a25e6f99e14773f2dd7cf62
parentd76ede2727110b24615780c0df910bd8e4f3e0c2
cow: Document config parameters

Make 'nbdkit --help --filter=cow null' give more details about the
cow filter.  Missed with the introduction of a config parameter.

Fixes: 90438c11
Signed-off-by: Eric Blake <eblake@redhat.com>
filters/cow/cow.c