write step-by-step instructions for obfsproxifying your debian bridge

Now that there's an obfsproxy deb, and it's in weasel's torproject repo (is this true?), it should be really easy for bridge operators to pop in obfsproxy too.

We should put some step-by-step instructions on the obfsproxy instructions page: add this line to your sources.list, apt-get install this, add this line to your torrc, make sure to set up port forwarding, mail your address to tor-assistants.