Just to get you going you have two simple approaches you can take.
First one is to just add this line to your main method:
Second approach is to add this standard log4j.properties (taken from the above mentioned guide) file to your classpath:
# Set root logger level to DEBUG and its only appender to A1.
# A1 is set to be a ConsoleAppender.
# A1 uses PatternLayout.
log4j.appender.A1.layout.ConversionPattern=%-4r [%t] %-5p %c %x - %m%n