Improve documentation for bc_bound() vs. bc_bound_hres()

[stephhazlitt]

The recommended usage of the two versions of bc line works is not well documented on the fxn pages or in the README, e.g., the quick but low resolution bc_bound() versus the very slow by high resolution bc_bound_hres(). This could be better documented, as some users can run into issues using bc_bound() with other higher resolution administrative layers. For example, a common use case:

library(bcmaps)
library(sf)

csd <- census_subdivision()
str(csd)
##sf [751 × 21] (S3: sf/tbl_df/tbl/data.frame)

#clipping out the water in the csd-level map with low res bc_bound()
csd_low <- st_intersection(csd, bc_bound())
str(csd_low)
##sf [897 × 22] (S3: sf/tbl_df/tbl/data.frame)

#clipping out the water in the csd-level map with high res bc_bound_hres()
csd_hi <- st_intersection(csd, bc_bound_hres())
str(csd_hi)
##sf [751 × 24] (S3: sf/tbl_df/tbl/data.frame)

[stephhazlitt]

Closed with #125.