documentation issue in README.md

[dale6john]

The example to create a proxy to rewrite headers didn't work for me. The documented:

proxy.on('proxyReq', function(proxyReq, req, res, options) {
proxyReq.setHeader('X-Special-Proxy-Header', 'foobar');
});

instead seems to work better as:

proxy.on('proxyReq', function(proxyReq, req, res, options) {
res.setHeader(header, "*");
});