[jdk11u] RFR: 8251551: Use .md filename extension for README [v2]

Mon Jun 20 08:29:46 UTC 2022

> backports https://bugs.openjdk.org/browse/JDK-8251551 as it's a low risk change

George Adams has refreshed the contents of this pull request, and previous commits have been removed. The incremental views will show differences compared to the previous content of the PR. The pull request contains one new commit since the last revision:

  Backport 6ed221cb9ad2e81d92dda0ef32095dda5d52cb85

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Changes:
  - all: https://git.openjdk.org/jdk11u/pull/47/files
  - new: https://git.openjdk.org/jdk11u/pull/47/files/ea6e99a7..61a3c4c7

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk11u&pr=47&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk11u&pr=47&range=00-01

  Stats: 0 lines in 0 files changed: 0 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u/pull/47.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u pull/47/head:pull/47

PR: https://git.openjdk.org/jdk11u/pull/47