git: openjdk/jdk8u-dev: 8251551: Use .md filename extension for README

[Zdenek Zambersky]

Changeset: 2f81fb4b
Author:    Zdenek Zambersky <zzambers at openjdk.org>
Date:      2023-11-28 10:37:30 +0000
URL:       https://git.openjdk.org/jdk8u-dev/commit/2f81fb4b586097e5cb3e139e2131dd7a5b6312a5

8251551: Use .md filename extension for README

Reviewed-by: phh
Backport-of: 4fbe635b21e3aba14dba760168a2f8965c7b29f5

- README
+ README.md