storage: Fix mention of disk pool default

The default disk storage pool type in XML is 'dos', not 'msdos'.
But tweak wording to keep the term 'msdos' in the text for the
sake of grep searches.
Signed-off-by: NEric Blake <eblake@redhat.com>
Reviewed-by: NJohn Ferlan <jferlan@redhat.com>

docs/storage.html.in

@@ -310,7 +310,7 @@
       on the size and placement of volumes. The 'free extents'
       information will detail the regions which are available for creating
       new volumes. A volume cannot span across 2 different free extents.
-      It will default to using <code>msdos</code> as the pool source format.
+      It will default to using <code>dos</code> as the pool source format.
     </p>
 
     <h3>Example pool input</h3>
@@ -357,8 +357,10 @@
       </li>
     </ul>
     <p>
-      The <code>dos</code> or <code>gpt</code> formats are recommended for
-      best portability - the latter is needed for disks larger than 2TB.
+      The formats <code>dos</code> ("msdos" in parted terminology,
+      good for BIOS systems) or <code>gpt</code> (good for UEFI
+      systems) are recommended for best portability - the latter is
+      needed for disks larger than 2TB.
     </p>
 
     <h3>Valid volume format types</h3>