readme typo

I was looking at the readme, and noticed that I couldn't find this method network.parse.private() in the code pycoin/networks/ParseAPI.py.

In the readme at line 58: "same_key = network.parse.private(key.wif())"

All I could find was "def private_key(): which seems to work.

I'd update it in a branch and create a PR but I don't have permissions.

Cheers!
--mark