Add ONS Open Geog API example

See merge request SERG/mapping-with-r!2

Open geog API example

See merge request twr1m15/mapping-with-r!1

# Resolve Conflicts:
#   README.md

# Conflicts:
#	README.md

script to download and pre-save boundary data for the examples. NB: the very large MSOA 'all areas' file is not stored on the repo due to size