Rename LICENSE.md → LICENSE to avoid broken formatting on gh

[zetok]

This change is 

[iphydf]

though I'd like to have all licenses be markdown at some point, so we can collect them all during website page build and display them there, with links to the repos that are governed by each license.

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Reviewed 2 of 2 files at r1. Review status: all files reviewed at latest revision, all discussions resolved.

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Comments from Reviewable

[cebe]

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Reviewed 2 of 2 files at r1. Review status: all files reviewed at latest revision, all discussions resolved, some commit checks failed.

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Comments from Reviewable

[zetok]

Deprecated by #38, thus closing.