Tell the world how to convert gigabytes to bytes with units(1) easily

It turns out that units(1) is not as horrible to use in scripts as I initially
thought. When the --terse flag is combined with an appropriate output format
(set via --output-format), units(1) is actually capable of producing very nice
results. For example:

    units -o %0.f -t '4 gigabytes' bytes

is just going to print out the expected value of 4294967296.

There is no time to waste. People have to know about it.

I am adding an example for this at the top of the examples section because
this is what users are most likely looking for.