More documentation and examples

[Moohan]

Hey, it would be great to have some more documentation in the form of examples (maybe as an article/vignette). I think the col_select is emphasised enough on the main README but I still see people writing code that doesn't use it... The various features (column selection, recid and partnership filtering) may get lost on the main README.

Now the files are using arrow/parquet, the really powerful feature is to read them as a 'dataset', (using as_dataframe = FALSE) i.e. Working with Arrow Datasets and dplyr. It would be great to have some examples showing that as it allows people to do filtering that isn't in-built efficiently e.g. filtering to all_population etc..

I'd be happy to work with someone on this and I'd also look to get some more 'full' examples (i.e. doing some analysis as well, slightly beyond the scope of slfhelper) on the LIST-examples repo where we have 'best-practice' code for common LIST analyses.