'getting started' vignette

[njtierney]

Still need to fill this in with more content from issues.

For example

• using gdam and vsizip and cgaz using geodata::gadm with geotargets #22
• using geotargets_option_set - Options makeover #45

This will resolve #17

[Aariq]

It's a good start! I think eventually we should add an example of how to change file type and pass GDAL options, but that could be in a separate PR if you'd rather.

[Aariq]

Is eval=FALSE just so CRAN doesn't complain? It might be better to precompute the vignette instead.

[njtierney]

Good idea with precomputing!

[Aariq]

Because of the trick to set root.dir to a temporary directory, you don't need tar_dir() at all I think. All examples have three chunks: one with echo: false to write the _targets.R file with tar_script(), one with eval: false to show the contents of _targets.R, and one with echo and eval true to run the pipeline and inspect results.

I didn't include much about the raster and vector GDAL options, because I don't have a good motivating example, but I did include examples of changing the driver and added an example with preserve_metadata = "zip".

[Aariq]

@njtierney, I think this is pretty much done. Can you take a look when you get a chance?