Document the new --only-write-batch=FILE option.

rsync.yo

@@ -380,6 +380,7 @@ to the detailed description below for a complete description.  verb(
      --list-only             list the files instead of copying them
      --bwlimit=KBPS          limit I/O bandwidth; KBytes per second
      --write-batch=FILE      write a batched update to FILE
+     --only-write-batch=FILE like --write-batch but w/o updating dest
      --read-batch=FILE       read a batched update from FILE
      --protocol=NUM          force an older protocol version to be used
      --checksum-seed=NUM     set block/file checksum seed (advanced)
@@ -1277,6 +1278,16 @@ dit(bf(--write-batch=FILE)) Record a file that can later be applied to
 another identical destination with bf(--read-batch). See the "BATCH MODE"
 section for details.
 
+dit(bf(--only-write-batch=FILE)) Works like bf(--write-batch), except that
+no updates are made on the destination system when creating the batch.
+This lets you transport the changes to the destination system via some
+other means and then apply the changes via bf(--read-batch).  Note that
+you can feel free to write the batch directly to some portable media: if
+this media fills to capacity before the end of the transfer, you can just
+apply that partial transfer to the destination and repeat the whole process
+to get the rest of the changes (as long as you don't mind a partially
+updated destination system while the multi-update cycle is happening).
+
 dit(bf(--read-batch=FILE)) Apply all of the changes stored in FILE, a
 file previously generated by bf(--write-batch).
 If em(FILE) is "-" the batch data will be read from standard input.