Pick transformation specific examples for 'using-xmaps'

[cynthiahqy]

Two types of data transformations using xmaps:

• nomenclature transformation -- what you really need the tidy nomenclature format for!
• aggregation/disaggregation (a bit meh, until you resolve hierarchical discrepancies?)

Examples:

• Use state-country example for aggregation/disaggregation (i.e. hierarchical nomenclature)
• product groups? trade data? // cross-country ex-post harmonisation?

Candidate examples:

• https://jforbes14.github.io/eechidna/articles/imputing-census-data.html
• NAICS/trade data

[cynthiahqy]

Candidate examples:

• https://jforbes14.github.io/eechidna/articles/imputing-census-data.html
• NAICS/trade data

[cynthiahqy]

Tracked in #117 instead.