The mongoimport utility does not work with external file sources such as a URI resource like you are trying to do.
In order to do what you want, "pipe" the input from another command like curl to mongoimport instead:
curl http://fromtheramp.com/temp/country.csv | \
mongoimport -d ramp -c country --type csv --headerline
Both mongoimport and mongoexport both work with STDIN/STDOUT as default unless you include an option such as --file. So omit that and work with STDIN instead.
As a non-csv example ( same principles apply though ) you can use the publicly accessible mongodb sample data set as a test:
curl https://raw.githubusercontent.com/mongodb/docs-assets/primer-dataset/dataset.json | \
mongoimport -d test -c restaurants --drop
Which hapilly imports that data, and a bit more effienctly than the manual page suggests you do it. Though you might want a local copy for testing.