Fix some trivial typos

Signed-off-by: Sam Kleinman <samk@10gen.com>
Document how to sort mongoexport results using -q

This should be mentioned in the docs; there's a StackOverflow question about that:
http://stackoverflow.com/questions/9005983/how-to-export-sorted-data-using-mongoexport

Signed-off-by: Sam Kleinman <samk@10gen.com>
minor: clarification for --sort option to mongoexport