Add blank spaces notice about 2 parameters version of Static.Serve

Use of encoding/csv in parsing of the routes file poses limit to the format of parameters passed to Static.Serve,
i.e. spaces between " and , are not insignificant in the parsing of csv values.

Adding spaces between " and , will result in error: bare " in non-quoted-field from encoding/csv.

http://golang.org/pkg/encoding/csv/