Add section on pre-built binaries to README

[JornVernee]

I've added a short section on where to find the pre-built binaries. I think building jextract is less important than the information on usage if people can get binaries, so I've moved the section on building and testing to the bottom.

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Progress

• Change must not contain extraneous whitespace
• Change must be properly reviewed (no review required)

Reviewers

• Athijegannathan Sundararajan (@sundararajana - Committer) ⚠️ Review applies to 9a98da4f

Reviewing

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Checkout this PR locally:
$ git fetch https://git.openjdk.org/jextract pull/84/head:pull/84
$ git checkout pull/84

Update a local copy of the PR:
$ git checkout pull/84
$ git pull https://git.openjdk.org/jextract pull/84/head

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Checkout this PR locally:
$ git pr checkout 84

View PR using the GUI difftool:
$ git pr show -t 84

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[sundararajana]

Looks good

[sundararajana]

could https://jdk.java.net/jextract/ be a link?

[sundararajana]

peridodically spelling

[openjdk]

@JornVernee This change now passes all automated pre-integration checks.

After integration, the commit message for the final commit will be:

Add section on pre-built binaries to README

Reviewed-by: sundar

You can use pull request commands such as /summary, /contributor and /issue to adjust it as needed.

At the time when this comment was updated there had been no new commits pushed to the master branch. If another commit should be pushed before you perform the /integrate command, your PR will be automatically rebased. If you prefer to avoid any potential automatic rebasing, please check the documentation for the /integrate command for further details.

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[JornVernee]

/integrate

[mlbridge]

Webrevs

• 01: Full - Incremental (1ba7f75e)
• 00: Full (4a8f808f)

[openjdk]

@JornVernee
Your change (at version 4a8f808) is now ready to be sponsored by a Committer.

[JornVernee]

/integrate

[openjdk]

@JornVernee
Your change (at version 1ba7f75) is now ready to be sponsored by a Committer.

[mcimadamore]

/sponsor

[openjdk]

Going to push as commit f70e8d2.

[openjdk]

@mcimadamore @JornVernee Pushed as commit f70e8d2.

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