Deploy docs update: SSH add-on

[gmartenscb]

The current documentation on "Retrieving SSH Credentials" references the Terminal & SSH addon.
While this is a viable add-on, community-wide it is suggested to use Advanced SSH & Web Terminal instead.

I think it is wise to also provide documentation for this add-on, as it is slightly different from the one provided.
And it gave me some (very minor) issues while setting it up myself.

1. The username has to be set to root (default is hassio).
2. The sftp flag has to be set to true (default is false, and true requires the username to be root).

[shannonhochkins]

Have updated & tested myself - all works fine

[gmartenscb]

Need a review? Can't really see where you did it in a PR / branch. Otherwise I can mark it as resolved.

[shannonhochkins]

It's all good, this PR has over 200 files changed which goes against everything I stand for, but that's open source for ya 😉 here's the link the doc changes you suggested!