Readme improvement

[zltnDC]

I was migrating an HTTP Server to FlyingFox and I encountered a client side error "Socket write failed". I spent some time to discover this line:

FlyingFox/FlyingFox/Sources/HTTPConnection.swift

Line 122 in ed86fc6

if !request.shouldKeepAlive {

The client app didn't send the "keepalive" header in requests. I think it would be great to mention "keepalive" in readme.

Thank you for this great lightweight server :)

[swhitty]

Do you think this is a bug where clients do not send Connection: keep-alive and FlyingFox is closing the connection too early?

Out of interest which HTTP Client were you using?