docs, ssh: unsupport password auth explicitly
docs, ssh: unsupport password auth explicitly

The issue with password auth is tracked in #1476 and #1477 .

Signed-off-by: Akihiro Suda <ea940da7e429af3d0d0c18296cabd0112a36bad5@lab.ntt.co.jp>

thaJeztah/cli,docker/cli,docker/cli,cpuguy83/cli,thaJeztah/cli,cpuguy83/cli