Notes on --transfers and B2

docs/content/b2.md

@@ -120,6 +120,16 @@ Rclone doesn't provide any way of managing old versions (downloading
 them or deleting them) at the moment.  When you `purge` a bucket, all
 the old versions will be deleted.
 
+### Transfers ###
+
+Backblaze recommends that you do lots of transfers simultaneously for
+maximum speed.  In tests from my SSD equiped laptop the optimum
+setting is about `--transfers 32` though higher numbers may be used
+for a slight speed improvement. The optimum number for you may vary
+depending on your hardware, how big the files are, how much you want
+to load your computer, etc.  The default of `--transfers 4` is
+definitely too low for Backblaze B2 though.
+
 ### API ###
 
 Here are [some notes I made on the backblaze