update README to be in markdown format

README.md

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+# HDCP Key Generation Example
+
+This script implements a simple version of the HDCP key generation algorithm in
+Python using the leaked HDCP master key (which is located in master-key.txt).
+
+```
+Usage: generate_key.py [options]
+
+Options:
+  -h, --help            show this help message and exit
+  -m FILE, --master=FILE
+                        load master key from FILE
+  -k, --sink            generate a sink key rather than a source key
+  --ksv=KSV             use a specific KSV expressed in hexadecimal
+  -j, --json            output key and KSV as JSON
+  -t, --test            generate source and sink keys and test they work
+```
+
+Examples:
+
+```console
+# Generate a sink key with KSV 0x54f0af39a8 and output the result in JSON
+./generate_key.py -k --ksv 54f0af39a8 -j
+
+# Generate a source key with a random KSV and output the result in a 
+# human-readable form
+./generate_key.py
+
+# Run a self-test to make sure the source a sink key generation is consistent
+./generate_key.py -t
+```
+