add a README

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+ciso is a simple commandline utility to compress PSP iso files.
+
+This package is a (currently incomplete) port of a package provided
+by Ubuntu: http://packages.ubuntu.com/natty/ciso
+
+# Usage
+
+To decompress a cso file:
+
+  ciso 0 infile.cso outfile.iso
+
+To compress an iso file:
+
+  ciso level infile.iso outfile.cso
+
+where level ranges from 1 (fast, poor compression) to 9 (slow, high
+compression).
+
+# WARNING
+
+Do Not Trust Your Data To This
+
+While it appears that iso -> cso -> iso roundtrips are lossless, the
+generated cso is broken and existing csos that I have are not
+recognized by the executable.
+
+Given the compilation warnings I get I am assuming it's buggy due to
+differences between Linux and MacOS libraries.