Exmaple using missing dataset

Frist step of the [example](https://github.com/ITSLeeds/cyclability#lts-data-from-r5) is loading data generated by `r5r_setup.R`

First step:
`leeds_lts = readRDS("r5r/r5r_lts_osmtags.Rds")`

Within `r5r_setp.R` this dataset is not created, rather a geojson is:
```
# export network with osm_id and LTS levels
r5r_lts_shp = street_network_to_sf(r5r_lts)
r5r_lts_edges = r5r_lts_shp$edges
r5r_lts_vert = r5r_lts_shp$vertices
# nrow(r5r_lts_shp) # 10134 edges
# saveRDS(r5r_lts_edges, "r5r/r5r_lts_shp.Rds") <--- Commented out!
sf::st_write(r5r_lts_edges, "r5r/r5r_lts_shp.geojson")
```
You can either use the geojson by changing the filepath in the example to `leeds_lts = readRDS("r5r/r5r_lts_osmtags.geojson")`

OR uncomment this line in `r5r_setup.R` --> # saveRDS(r5r_lts_edges, "r5r/r5r_lts_shp.Rds")

Both the .geojson & .Rds are the same - it does not matter which is loaded.


Apart from that - everything runs smoothly and I have been able to reproduce plots!