Added documentation regarding CA pinning
Added documentation regarding CA pinning

Refs #2294

yacloud-io/teleport,gravitational/teleport,yacloud-io/teleport,yacloud-io/teleport,gravitational/teleport,yacloud-io/teleport,gravitational/teleport,gravitational/teleport,yacloud-io/teleport,gravitational/teleport,gravitational/teleport,yacloud-io/teleport,yacloud-io/teleport