RFR: Update README.md

[Jesper Wilhelmsson]

Added todo item

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Commit messages:
 - Update README.md

Changes: https://git.openjdk.java.net/guide/pull/55/files
 Webrev: https://webrevs.openjdk.java.net/?repo=guide&pr=55&range=00
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/guide/pull/55.diff
  Fetch: git fetch https://git.openjdk.java.net/guide pull/55/head:pull/55

PR: https://git.openjdk.java.net/guide/pull/55