Add ZhangX_2015 study

[schifferl]

Per https://support.bioconductor.org/p/9149297/, a user would like us to add the ZhangX_2015 study (PRJEB6997) to curatedMetagenomicData – just adding a note here if anyone has time for curation.

[edoardopasolli]

@paolinomanghi I remember that we had this dataset at a certain point?

[paolinomanghi]

I would like to add it, as soon the paper gets published and the storage is collaborative

[schifferl]

@paolinomanghi, from the post it seems like the paper has been published (https://www.nature.com/articles/nm.3914).