add required packages to README

[lecy]

Consider adding packages to GitHub launch option:

Shiny app exploring Edinburgh traffic collision data. View from R with:

check_and_install <- function( package )
{ if (!package %in% installed.packages()) install.packages(package) }

check_and_install( "dplyr" )
check_and_install( "DT" )
check_and_install( "ggplot2" )
check_and_install( "htmltools" )
check_and_install( "leaflet" )
check_and_install( "rcharts" )
check_and_install( "shiny" )

shiny::runGitHub("blmoore/blackspot")