newfs_msdos.8: example for specific cluster size

The usual use case in 2024 for newfs_msdosfs is creating filesystems on SD cards
for older hardware. In most tutorials, they call the cluster size "allocation
size". Therefore, add a small note next to cluster size that it is also called
allocation size, and add an example for how to do this.

Reviewed by:	jhb
Pull Request:	freebsd/freebsd-src#1045

sbin/newfs_msdos/newfs_msdos.8

@@ -23,7 +23,7 @@
 .\" OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 .\" IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 .\"
-.Dd June 14, 2018
+.Dd January 12, 2024
 .Dt NEWFS_MSDOS 8
 .Os
 .Sh NAME
@@ -134,7 +134,7 @@ File system block size (bytes per cluster).
 This should resolve to an
 acceptable number of sectors per cluster (see below).
 .It Fl c Ar cluster-size
-Sectors per cluster.
+Sectors per cluster, also called allocation size.
 Acceptable values are powers of 2 in the range
 1 through 128.
 If the block or cluster size are not specified, the code
@@ -224,6 +224,12 @@ Create a file system, using default parameters, on
 newfs_msdos /dev/ada0s1
 .Ed
 .Pp
+Create a FAT32 filesystem with a 32K allocation size on
+.Pa /dev/mmcsd0s1 :
+.Bd -literal -offset indent
+newfs_msdos -F 32 -A -c 64 /dev/mmcsd0s1
+.Ed
+.Pp
 Create a standard 1.44M file system, with volume label
 .Ar foo ,
 on