Update readme from website documentation

README.md

@@ -6,5 +6,43 @@ It contains several webapps for different flavors of the Sankey chart.
 
 The charts are based on the [Google Charts library](https://developers.google.com/chart/) and require internet access.
 
+![An example of a sankey chart.](_img/example.png)
+
+
+## Description
+
+Sankey charts are used when you want to show a n-to-n mapping between
+two entities (e.g., countries and continents) or paths through several
+states (customer journey in an e-commerce website). The arrow widths are
+proportional to the flow's volume. The entities/states are usually
+represented in layers.
+
+## Installation Notes
+
+The plugin can be installed from the Plugin Store or via the zip
+download (see above).
+
+*Reminder:* A custom chart is an additional way to visualize information
+about a dataset, custom charts appear in the 'other' set of charts on a
+dataset.
+
+## Components
+
+### Static Sankey
+
+![Static sankey](_img/static_sankey.png)
+No processing is done on the data, states are rendered using weighted arrows.
+
+### Browsable Sankey
+
+![Browsable sankey](_img/browsable_sankey.png)
+
+This Sankey chart focuses the reprentation on a specific state and only renders the predecessors the successors. If a state is both a predecessor and a successor, it is considered as two distinct nodes (no
+cycles are possible; they are often not interesting in the case of flow visualization).
+
+In this mode, the sankey chart is browsable: you can click on any predecessor or sucessor and it will re-render the chart with this state as the central node.
+
+This mode is particularly suited for large sankey graphs or cyclic ones.
+
 ## License
 This project is licensed under the Apache Software License.