RFR: 6835: Adding developer guide for getting started with development

[Marcus Hirt]

On Fri, 12 Jun 2020 13:32:40 GMT, Alex Ciminian <github.com+348973+cimi at openjdk.org> wrote:

>> Hmm. Interesting. And you did set the active platform properly?
>
> I have the active platform set to this:
> 
> ![Screenshot 2020-06-12 at 13 55
> 18](https://user-images.githubusercontent.com/348973/84505203-39fa8980-acb5-11ea-8815-cfd4663d0805.png)
> I can build `core` without problems so I guess that's fine?
> 
> I've also tried the 2020-03 configuration but that was yielding many more errors, so I switched back to this.

Hmm, you should not have any problems with 2020-03. Photon is in queue for getting dropped eventually.

![image](https://user-images.githubusercontent.com/16906077/84510354-51da0980-acc5-11ea-964f-865a22eb6dd3.png)

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PR: https://git.openjdk.java.net/jmc/pull/82