* Change sshd port from 22 to 2222 in README.md

According to https://github.com/devcontainers/features/blob/e90f4f9e0a327466254f3f1693fbe75aaa2a862f/src/sshd/install.sh#L12 the default port is 2222 and not 22 as previously documented. Forwarding port 22 does not in fact work.

* Changed sshd port in NOTES.md