add note on ruby -l switch

Quite a useful switch for one-liners

sheets/ruby

@@ -13,6 +13,10 @@ ruby -e 'puts "Hello world"'
 #  end
 ruby -ne 'puts $_' file.txt
 
+# Beware that with the -n switch $_ contains newline character in the end.
+# With the addition of -l switch each line read has the newline character removed.
+ls | ruby -lne 'File.rename($_, $_.upcase)'
+
 # The -p switch acts similarly to -n, in that it loops over each of the lines in the input
 # after your code has finished, it always prints the value of $_
 # Example: replace e with a