RFR: CODETOOLS-7903131: missing LICENSE file

[Jonathan Gibbons]

Please review a change to add a missing LICENSE file.

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Commit messages:
 - CODETOOLS-7903131: missing LICENSE file

Changes: https://git.openjdk.java.net/doccheck/pull/2/files
 Webrev: https://webrevs.openjdk.java.net/?repo=doccheck&pr=2&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903131
  Stats: 347 lines in 1 file changed: 347 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/doccheck/pull/2.diff
  Fetch: git fetch https://git.openjdk.java.net/doccheck pull/2/head:pull/2

PR: https://git.openjdk.java.net/doccheck/pull/2