Add sha256 and sha512 checksums

That should suffice...

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
diff --git a/HOWTO b/HOWTO
index 58e1281..21ba960 100644
--- a/HOWTO
+++ b/HOWTO
@@ -588,6 +588,10 @@
 			crc7	Use a crc7 sum of the data area and store
 				it in the header of each block.
 
+			sha512	Use sha512 as the checksum function.
+
+			sha256	Use sha256 as the checksum function.
+
 			null	Only pretend to verify. Useful for testing
 				internals with ioengine=null, not for much
 				else.