x/crypto/ssh: Semantics of Conn.Wait and Conn.Close unclear in docs

[darkfeline]

The semantics of Conn.Wait and Conn.Close are unclear as of the docs currently.

https://pkg.go.dev/golang.org/x/crypto/ssh?tab=doc

	// Close closes the underlying network connection
	Close() error

	// Wait blocks until the connection has shut down, and returns the
	// error causing the shutdown.
	Wait() error

Is it necessary to call both, and in which order, or is just Close enough?

[cagedmantis]

/cc @hanwen @FiloSottile