message: readme: update for new test client and server
diff: To run test programs (neqo-client and neqo-server):
  * `cargo build`
  -* `./target/debug/neqo-server 12345 -k key -d ./neqo-crypto/db`
  +* `./target/debug/neqo-server 12345 -k key -db ./neqo-crypto/db`
  * `./target/debug/neqo-client 127.0.0.1 12345 --db ./neqo-crypto/db`
  +
  +or
  +
  +* `cargo build`
  +* `./target/debug/neqo-http3-server -p 12345 --db ./neqo-crypto/db`
  +* `./target/debug/neqo-http3-client http://127.0.0.1:12345/ --db ./neqo-crypto/db`
  +
  