Add shebang to r scripts, create .gitignore

add shebang to make r scripts executable from command line. add gitignore, ignore csv and RDS files since they can be produced locally using the provided r scripts

r/ExtractFromXML.R

+#!/usr/bin/env Rscript
+
 library(xml2)
 
 data <- read_xml("../data/Wikipedia-20181120103842.xml")