RFR: 7903802: apidiff: minor doc and related updates [v2]

[Jonathan Gibbons]

> Please review some minor doc changes for apidiff

Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:

  update copyright year

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Changes:
  - all: https://git.openjdk.org/apidiff/pull/4/files
  - new: https://git.openjdk.org/apidiff/pull/4/files/6b530694..a01c7502

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=apidiff&pr=4&range=01
 - incr: https://webrevs.openjdk.org/?repo=apidiff&pr=4&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/apidiff/pull/4.diff
  Fetch: git fetch https://git.openjdk.org/apidiff.git pull/4/head:pull/4

PR: https://git.openjdk.org/apidiff/pull/4