[jdk8u-dev] RFR: 8251551: Use .md filename extension for README

[Andrew John Hughes]

On Tue, 21 Jun 2022 07:52:23 GMT, George Adams <duke at openjdk.org> wrote:

> Backports https://bugs.openjdk.org/browse/JDK-8251551 as it's a low-risk change and generally improves the readability/usability in GitHub.
> 
> Currently, I've just converted the README to markdown format and added a little syntax highlighting. I'm not sure if people would like me to go one step further and rip out the mercurial/nested repo references?

I think we need to bring in the changes to convert to markdown first (notably [JDK-8139668](https://bugs.openjdk.org/browse/JDK-8139668) and [JDK-8176509](https://bugs.openjdk.org/browse/JDK-8176509)) before doing this. 

Also, this patch looks to be removing the old file and adding a new one, when it should be a rename. That makes it hard to see what has actually changed.

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Changes requested by andrew (Reviewer).

PR: https://git.openjdk.org/jdk8u-dev/pull/75