virt-df: Re-add documentation for --csv option.

The documentation for the --csv option disappeared between 1.6 and 1.8
when we rewrote virt-df in C.  Re-add it from 1.6 sources.
(cherry picked from commit 01f6bce19dbfaf42fa4908683f3cc8785585d023)

diff --git a/df/virt-df.pod b/df/virt-df.pod
index 65d78a1..9d05ac9 100755 (executable)
--- a/df/virt-df.pod
+++ b/df/virt-df.pod
@@ -85,6 +85,12 @@ connect to the default libvirt hypervisor.
 If you specify guest block devices directly (I<-a>), then libvirt is
 not used at all.
 
+=item B<--csv>
+
+Write out the results in CSV format (comma-separated values).  This
+format can be imported easily into databases and spreadsheets, but
+read L</NOTE ABOUT CSV FORMAT> below.
+
 =item B<-d> guest
 
 =item B<--domain> guest