[crac] Early-Access Builds

[Anton Kozlov]

Hi,

I've added a link to the CRaC early access builds to the wiki [1]:

https://github.com/CRaC/openjdk-builds/releases

This is a prerequisite for the "Testing" subsection under the "Contributing".
I linked [2], but something more focused on the OpenJDK testing would suit
better.

Thanks,
Anton

[1]: https://wiki.openjdk.java.net/display/crac
[2]: https://github.com/CRaC/docs/blob/master/STEP-BY-STEP.md