Update readme

README.md

@@ -10,7 +10,7 @@ pip install git+http://git.wrl.unsw.edu.au:3000/danh/scaling.git
 
 ## Usage
 
-```sh
+```python
 >>> from scaling import Froude
 >>> froude = FroudeConverter()
 
@@ -27,9 +27,44 @@ pip install git+http://git.wrl.unsw.edu.au:3000/danh/scaling.git
 'L^2 M^1 T^-2'
 ```
 
+Dataframes are also accepted, and specific units can be specified for the values in the index.
+
+```python
+>>> T = 2
+>>> H = 100
+
+>>> # Generate regular waves with height=100mm, and period=2s
+>>> t = np.arange(0, 10.1, 0.1)
+>>> eta = 0.5 * H * np.sin(t * 2 * np.pi / T)
+
+>>> df_model = pd.DataFrame(index=t, data=eta)
+>>> df_model.columns = ['$\eta$ (mm)']
+>>> df_model.index.name = 'Time (s)'
+
+>>> df_model.plot()
+```
+
+![](doc/model.png#0)
+
+```python
+>>> # Convert to prototype dimensions, with length scale=25
+df_proto = froude.model_to_proto(
+    df_model,
+    length_scale=25,
+    input_unit='mm',
+    target_unit='m',
+    index_input_unit='s',
+    index_target_unit='s')
+
+df_proto.columns = ['$\eta$ (m)']
+df_proto.plot()
+```
+![](doc/proto.png#0)
+
+
 `scaling` uses `pint` for unit and dimension conversions. `pint` is able to interpret a wide range of different input units.
 
-```sh
+```python
 >>> # Convert water head model value (mm) to prototype pressure value (kPa)
 >>> froude.model_to_proto(10, length_scale=100, 'mm.H20', 'kPa')
 9.80665