Output notice when a non-stable version of ghost-cli was used to install

[ErisDS]

Pretty much anyone who setup ghost using old versions of ghost-cli are going to have some sort of issue with their install being different to things in 1.0.0.

We know what version of Ghost CLI was used to install a particular ghost instance because it's very cleverly stored in .ghost-cli, so that in future, we can do migrations.

We have no intention of implementing pre 1.0.0 migrations though:

• If you installed with < beta.5 you have to install from scratch
• If you installed with beta.6 - you'll need to fix your nginx config
• If you installed with > beta.5 < rc.3 - you'll need to run the command to fix renewal

To help users sort this out, we'll add a message to ghost upgrade, where the .ghost-cli version is < 1.0.0 (the real release!) that says:

"Ghost was installed with Ghost-CLI v1.0.0-xxx, please see for additional steps needed to ensure your site continues to work."

The docs link will contain steps to perform a reinstall as safely as possible, and a couple of additional notes for how to fix anything installed with beta.6 or onwards as that is straightforward.