Docs: Add license to block preceding revision placement

[psibre]

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The documentation on revisions currently states that the revision "is inserted inserted underneath the homepage/url/sha256 block."

However, when I follow these instructions and add a revision to a formula, inserting it underneath the sha256 line (but above the license), the edited formula does not pass the audit:

$ brew audit --strict --online trivy
trivy
  * line 7, col 3: `license` (line 7) should be put before `revision` (line 6)
Error: 1 problem in 1 formula detected.

To clarify the relevant documentation, the license should be listed as part of the block beneath which the revision must be placed.

[MikeMcQuaid]

Thanks so much for your first contribution! Without people like you submitting PRs we couldn't run this project. You rock, @psibre!