Add more links to the changelog and blog

[Rylan12]

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We've received some blowback due to the short turn around time between Homebrew 2.6.0 and 2.7.0. 2.7.0 was the release that disabled brew cask commands, so 20 days didn't seem to be quite long enough for the entire community to adapt (namely, some ansible modules weren't updated in time which is causing breakage).

My personal opinion is that 20 days was a tad short for such a major change, but that's irrelevant to this PR (to be clear, not trying to blame any one person for this, it's simply a product of the way we do releases). Regardless of that, I think there are a few places where we could do some work to increase visibility for these releases.

This PR attempts to increase visibility in two ways:

1. Add a link to the Homebrew Blog to the release notes. It's easy for a user to come across the brew repo and, therefore, the release notes. Only the dedicated users who are really trying will be able to find the blog, though. I think we should add a link to the top of our release notes that links directly to the blog (this already exists in our unused CHANGELOG.md file). For now, I added this to all invocations of brew release-notes. I can, if desired, add an e.g. --major-minor flag to only add this line on major or minor releases (alternatively, there can be some autodetection done on the end_ref if it's passes).
2. Add links and clearer output to brew update. This PR will now display a message at the very bottom of the brew update output if Homebrew was updated to a new tag. This output will include a link to the release notes. If it's a major or minor release, a link to the blog will be added as well.

[BrewTestBot]

Review period will end on 2020-12-24 at 17:16:41 UTC.

[reitermarkus]

short turn around time between Homebrew 2.6.0 and 2.7.0

That's exactly why I think we should deprecate by giving a date instead of on the next “major” version.

[Rylan12]

That's exactly why I think we should deprecate by giving a date instead of on the next “major” version.

@reitermarkus I think you should open a separate issue to address this. I don't want this PR to be a discussion about whether the 2.7.0 release was right/wrong or any of that stuff. I was simply using that as an example to illustrate why I think this is a good idea (which I think is the case regardless of what we do in the future regarding deprecations and whatnot)

[MikeMcQuaid]

Thanks for this @Rylan12, good ideas here!

[BrewTestBot]

Review period ended.

[MikeMcQuaid]

What is (Date.today << 1) doing? A variable would also make this more obvious, I think. Date.today - 1.month work?

[Rylan12]

Doesn't work:

Error: undefined method `month' for 1:Integer

I'll extract to a variable one_month_ago

[MikeMcQuaid]

Nice work @Rylan12! Please be around to keep an eye for any issues when merging this; it's worth being scared of any changes to the updater code 😁

[Rylan12]

Sounds good. I'm going to merge now. I'll be available for several hours to deal with immediate issues that pop up.