Confusing message about SFTP mode in WordPress

[stevector]

I did a fresh installation of WordPress using this plugin. Doing so eliminates the capacity to use SFTP mode. But still, we provide an in-admin message directing people to use SFTP mode.

I think we should resolve this by

• altering this message (which is generated here in our mu plugin)
• and linking to https://docs.pantheon.io/github-application#no-on-server-development--sftp-mode