RFR: Added section for newcomers [v7]

[Jesper Wilhelmsson]

On Thu, 3 Dec 2020 08:33:34 GMT, Alan Bateman <alanb at openjdk.org> wrote:

>> Jesper Wilhelmsson has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Less choking on coffee
>
> src/index.md line 35:
> 
>> 33: ### 2. Socialize your change
>> 34: 
>> 35: Once the OCA is signed, please restrain your urge to create a PR just a little while longer. In order to prepare the community for your patch, please socialize your idea on the relevant [mailing lists](#mailing-lists). To understand the criteria by which your patch is going to be judged, please read [_Why is My Change Rejected?_](#why-is-my-change-rejected) below. In short, hidden constraints and assumptions, stability and quality, maintainability, compatibility, and conformance to specifications must be considered before your PR is ready to be submitted. If you don't understand the constraints for acceptance, you might be surprised when your PR is rejected.
> 
> I think proposals for API additions need to be called out here as a good example of something that needs discussion, and maybe agreement in principle, before going near code.

I've added a sentence to hi-light API changes.

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PR: https://git.openjdk.java.net/guide/pull/38