Add extended usage

README.md

@@ -17,3 +17,41 @@ Units.RealWorld to configure prefixes that aren't normally used.
 4.0 m
 </code>
 </pre>
+Unit.Units defines SI units, which are looked up by symbol.
+
+<pre>
+<code lang=python>
+>>> q = Quantity(1.0, "MV")
+>>> q
+1.0 MV
+>>> q = Quantity(1000000, 'V')
+>>> q
+1.0 MV
+>>> q.to('V')
+1000000.0
+</code>
+</pre>
+Many simple conversions are also provided
+
+<pre>
+<code lang=python>
+>>> volts = Quantity(10, 'V')
+>>> amps = Quantity(100, 'A')
+>>> volts * amps
+1.0 kW
+>>> volts / amps
+100.0 mΩ
+</code>
+</pre>
+You can define your own units. We can get frames per second by defining frames.
+
+<pre>
+<code lang=python>
+>>> frame = Unit.Unit('f', "frame")
+>>> frames = Quantity(432000, "frame")
+>>> runningTime = Quantity(120 * 60, 's')
+>>> fps = frames / runningTime
+>>> fps
+60.0 f/s
+</code>
+</python>