docs: update license documentation

[Rylan12]

• Have you followed the guidelines in our Contributing document?
• Have you checked to ensure there aren't other open Pull Requests for the same change?
• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes? Here's an example.
• Have you successfully run brew style with your changes locally?
• Have you successfully run brew tests with your changes locally?

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Update documentation for the new license syntax.

Changes

• Add docs/License-Guidelines.md to describe the new syntax
• Add License Guidelines page to docs/README.md
• Update docs/Formula-Cookbook.md to describe the new syntax and link to the license guidelines page
• Update license documentation in formula.rb to be reflected here
  • Change :all to :all_of and :any to :any_of (I must have missed a few last time)
  • Add a link to the License Guidelines page
  • Add a nested example to align with the License Guidelines

[jonchang]

Looks good! Does it make sense to mention HOMEBREW_FORBIDDEN_LICENSES somewhere in these docs?

[Rylan12]

Looks good! Does it make sense to mention HOMEBREW_FORBIDDEN_LICENSES somewhere in these docs?

Probably. Does it make sense to add this to the License Guidelines page? This might fit better in the "Users" section rather than the "Contributors" section of the docs.

[MikeMcQuaid]

Does it make sense to add this to the License Guidelines page?

I think so! It's already documented for users in the manpage.

[Rylan12]

I added a section to the License Guidelines page with some more information about HOMEBREW_FORBIDDEN_LICENSES

[Rylan12]

I took a second pass through what I wrote and clarified some wording (and fixed some typos). Assuming no one else has any comments, I'll go ahead and merge this tomorrow morning.

[maxim-belkin]

👍 Only one comment but, otherwise, LGTM!