suggest use of superctr adpcm program instead

todo: change examples and such to use it

Author: freem

tools/readme.txt

@@ -14,3 +14,6 @@ genSSGSquareTable.lua	Lua (5.1) script for generating a SSG tone period table.
 [Notes]
 Tools in here may have a different license than the main library.
 I will try and be better about being consistent with licenses.
+
+The ADPCM-A tool is deprecated, as superctr's "adpcm" tool can handle both
+ADPCM-A and B within the same binary. See https://github.com/superctr/adpcm