Add MIT license file

[kitsuyui]

Summary

• Add the root MIT license text matching the package.json license declaration.
• Give GitHub a physical license file to detect and display for the repository.

Checks

• typos LICENSE
• git diff --check

[github-actions]

🎉 Happy commit!

• dogfooding: PR Add MIT license file #827 always celebrates.
• dogfooding: b87db6ab3de93a40fa900d82fe2e213e26516dfc always celebrates.

[github-actions]

Code Metrics Report

	main (45435c8)	#827 (1e1a68f)	+/-
Coverage	99.0%	99.0%	0.0%
Code to Test Ratio	1:0.5	1:0.5	0.0
Test Execution Time	1s	1s	0s

Details

  |                     | main (45435c8) | #827 (1e1a68f) | +/-  |
  |---------------------|----------------|----------------|------|
  | Coverage            |          99.0% |          99.0% | 0.0% |
  |   Files             |              5 |              5 |    0 |
  |   Lines             |            107 |            107 |    0 |
  |   Covered           |            106 |            106 |    0 |
  | Code to Test Ratio  |          1:0.5 |          1:0.5 |  0.0 |
  |   Code              |           1386 |           1386 |    0 |
  |   Test              |            758 |            758 |    0 |
  | Test Execution Time |             1s |             1s |   0s |

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Reported by octocov