Print ‘update available’ message.

[alloy]

I feel like we discussed this before, but it was probably in Slack and so now I’m going to record this.

I think it would be helpful for Hokusai to check if updates are available, seeing as sometimes it’s important to update and deploy time should be as smooth as possible. Something like:

$ hokusai […]
[!] An update is available and may be required to perform further operations. Install with: $ curl -O […]

There are some considerations to make, such as:

• should this check happen synchronously?
• should this check happen on launch?
• should this check happen every time or eg once a day?