Fix example in README

Author: rjcorwin

README.md

@@ -4,8 +4,8 @@ A CLI to push data from a pipe to a csv. Contains support for streams.
 
 Example:
 ```
-> echo "42" | opk-cli-simple-csv/push
-> echo "44" | opk-cli-simple-csv/push
+> echo "42" | opk-cli-simple-csv/push output.csv
+> echo "44" | opk-cli-simple-csv/push output.csv
 > cat output.csv
 2015-06-16 00:31:47,42
 2015-06-16 00:31:48,44