Add std/bzip2/README.md note about bzip 1
diff --git a/std/bzip2/README.md b/std/bzip2/README.md
index 24ccfd4..5e0bcf0 100644
--- a/std/bzip2/README.md
+++ b/std/bzip2/README.md
@@ -84,7 +84,10 @@
(a) A 16-bit magic number "BZ" meaning the start of the bzip2 file.
-(b) The 'h' byte means Huffman compression.
+(b) The 'h' byte means Huffman compression. The original bzip (as in, without
+the "2" in "bzip2") used a '0' byte here to indicate arithmetic codes instead
+of Huffman codes, but arithmetic/bzip was not widely used because of patent
+concerns. This package (and worked example) only considers Huffman/bzip2.
(c) The '9' byte means the uncompressed block size ranges up to 900000
(inclusive).
