Add a way to display changes to the kit

[unixorn]

Feature Request

Based on discussion in https://github.com/unixorn/zsh-quickstart-kit/issues/205, we need a way to display changes to the kit like updates to the plugin list.

Describe the solution you'd like

Need to determine a way to display changelog increments to users without being spammy.

It should:

• Allow users to disable and enable change notifications with a zqs command. Maybe zqs change-notifications yes|no
• Only display a given change notice once, the first time the user logs in after the kit is updated.

[neiromaster]

The idea of displaying a list of changes is good, but what should it show? The simplest option is to display a list of commits. Is it informative enough? For example, I'd be interested to see a list of new/removed plugins additionally, if it's possible. The idea of enabling with zqs change-notifications yes|no is great!

[unixorn]

I'm trying to think of a generic way for me to be able to notify on anything.

I want to be able to say "swapped from using foo-plugin in the standard list to bar-plugin" or "security fix xyz"

I also don't want to add a lot of overhead, or have it spew an error message if someone is disconnected from internet.

I was thinking about adding a notifications directory to the repo, and track what they've seen with a cookie file, but then the kit has to know where it's checkout is, in a cross-platform way.

[unixorn]

And I also want it to not add noticeably to startup time, so it's a trickier problem than I thought.