separate contribution section describing writing of `wrapper.(py|R)`

[dlaehnemann]

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The contribution docs are currently being extended and improved by @mbhall88 in PR #380. During the review of this process, we re-identified a long standing shortcoming of the contribution docs, that we cannot quickly address during this review: the contribution docs should have a dedicated section on how to write a good wrapper.py/wrapper.R, with both hard requirements and useful tips and tricks. So, for now, we'll document that need here for anybody to pick up!

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This issue was marked as stale because it has been open for 6 months with no activity.

[github-actions[bot]]

This issue was closed because it has been inactive for 1 month since being marked as stale. Feel free to re-open it if you have any further comments.