Update Project README to support markdown about ike-scan

[royhills]

I didn't realise github supported a markup language for the README file. It certainly makes the project look much better, and I think it would be a good thing to do.

The only things to consider are whether it's best to have a separate README.md and README. Automake likes to see a file called README, but I guess github needs the .md extension to render the markup correctly. It would probably be easy to have a makefile rule to generate the text file from the markdown one sed or grep though.

But, yes, let's do it. Markdown formatted readme's look much better than plain text ones.