time: document how to render milli/micro/nano in time.Format #10963
Description
The reference time described in the docstring for Format doesn't provide a value for nanoseconds. This hides the functionality provided by the Format function to render milli, micro and nanoseconds.
This has led to some confusion that Format can't handle sub-second precision: https://groups.google.com/forum/#!topic/golang-nuts/TIinEnPu5wE
One option for a solution might just be to add '.000000000' to the reference time in the doc comment.