README.rst - updates default algorithms from MD5 to SHA256 and SHA512

Author: kieranjol

README.rst

@@ -65,7 +65,7 @@ machine. You can do that with the ``--processes`` option:
     bagit.py --processes 4 /directory/to/bag
 
 To specify which checksum algorithm(s) to use when generating the
-manifest, use the --md5, --sha1, --sha256 and/or --sha512 flags (MD5 is
+manifest, use the --md5, --sha1, --sha256 and/or --sha512 flags (SHA256 and SHA512 are
 generated by default).
 
 ::