RFR: Added section on maintainer-pain [v2]

[Jesper Wilhelmsson]

On Mon, 16 Nov 2020 19:39:08 GMT, Igor Ignatyev <iignatyev at openjdk.org> wrote:

>> Jesper Wilhelmsson has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Refer to ProblemList section
>
> @JesperIRL , looks good to me in general. however, I'm not sure that every occurrence of `maintainer-pain` should be a reference, usually, it's enough to have just 1st appearance as a reference.
> 
> -- Igor

Just for the record, the maintainer-pain label and the use of it was discussed on jdk-dev here: https://mail.openjdk.java.net/pipermail/jdk-dev/2018-September/001929.html

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PR: https://git.openjdk.java.net/guide/pull/37