Add documentation for retaining properties with geo2topo

[omundy]

Before the name change from topojson to geo2topo (per many threads on stackoverflow) it was possible to retain properties from the original geojson file with the following

topojson in.json -o out.json -p prop1,prop2

Can geo2topo still do this? It would be great if the documentation covered this.

[mbostock]

Any properties and identifiers of input feature objects are propagated to the output. If you want to transform or filter properties, try ndjson-cli as demonstrated in Command-Line Cartography.

[woodz-]

Is there a test for the

properties are propagated

statement?

14