help: document wire protocol "handshake" protocol
There isn't a formal handshake protocol in the wire protocol. But
clients almost certainly need to perform particular actions before they
can communicate with a server optimally. So document what that is
so people understand what's going on at connection establishment time.
To run the tests, do:
cd tests/
python run-tests.py
See https://mercurial-scm.org/wiki/WritingTests for
more information on writing tests.