added readme

README.md

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+# shuffle3 - 3 stage byte shuffler
+
+Deterministically and reversably shuffle a file's bytes around.
+
+## Shuffling
+Shuffle a file in place
+
+``` shell
+$ shuffle3 -s file
+```
+
+## Unshuffling
+Unshuffle a file in place
+
+``` shell
+$ shuffle3 -u file
+```
+
+## Other options
+Run with `--help` for more options.
+
+# License
+GPL'd with <3