Create retire-unpublished.md

I have not added this file to the toc until it's been reviewed!!! Please add on merge if approved @paolap or @chloemackallah 

I am not happy with the number rendering here where I've done 'custom' things, if you wish to rework the numbered lists I think it'd help?

This commit attempt to address most of Sharon's issues raised in #10

Governance/retire/retire-unpublished.md

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+# Use case: unpublished data
+
+This use case addresses the plethora of data that is associated with published data creation. That is, storage use including, but not limited to:
+
+- Model configuration data
+- Failed model run output
+- Successful model run output
+- Data prepared for collaborative sharing but not publication/DOI
+- Intermediate data products
+
+How each of these scenarios is handled will typically be determined on a project basis, with a view to the importance of **reproducibility** and considering relative **compute or storage costs**.
+
+## Suggested procedures
+
+**If compute is readily available but storage is limited**
+
+1. Maintain a database or wiki of model runs
+2. Create zip archives of model configurationsand move to slow access tape storage if they are required to be kept for reproducibility 
+3. If model run failed, remove data immediately
+4. If model run was successful and post-processing has been completed (and if bit-reproducibility across systems is not a concern), then data can be removed, perhaps after an initial quarantine period for data validation
+5. Intermediate data products and collaborative data can be retired at the end of their active projects, following a quaratine period
+
+5a. Some intermediate data may not have a logical project end, such as regridded CMIP data - such data might follow a similar approach as the replciated data use case.
+
+**If compute is limited but deep storage is readily available**
+
+Repeat steps 1-3 as above.
+
+4. Following post-processing and validation, or at project close, data should be tarred and trasnferred to a deep storage system