qemu-img: clarify src_cache option documentation

The source cache option takes the same values as the cache option.  The
documentation reads a little strange because it starts with "In contrast
the src_cache option ...".  The fact that this is comparing with the
previous documented option (the 'cache' option) is implicit.  Readers
may be confused, especially if they jump to src_cache without reading
cache documentation first.

Suggested-by: Jeff Nelson <jenelson@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>

qemu-img.c

@@ -95,7 +95,8 @@ static void QEMU_NORETURN help(void)
            "  'cache' is the cache mode used to write the output disk image, the valid\n"
            "    options are: 'none', 'writeback' (default, except for convert), 'writethrough',\n"
            "    'directsync' and 'unsafe' (default for convert)\n"
-           "  'src_cache' in contrast is the cache mode used to read input disk images\n"
+           "  'src_cache' is the cache mode used to read input disk images, the valid\n"
+           "    options are the same as for the 'cache' option\n"
            "  'size' is the disk image size in bytes. Optional suffixes\n"
            "    'k' or 'K' (kilobyte, 1024), 'M' (megabyte, 1024k), 'G' (gigabyte, 1024M),\n"
            "    'T' (terabyte, 1024G), 'P' (petabyte, 1024T) and 'E' (exabyte, 1024P)  are\n"

qemu-img.texi

@@ -73,8 +73,9 @@ specifies the cache mode that should be used with the (destination) file. See
 the documentation of the emulator's @code{-drive cache=...} option for allowed
 values.
 @item -T @var{src_cache}
-in contrast specifies the cache mode that should be used with the source
-file(s).
+specifies the cache mode that should be used with the source file(s). See
+the documentation of the emulator's @code{-drive cache=...} option for allowed
+values.
 @end table
 
 Parameters to snapshot subcommand: