Update vega3-extension README

packages/vega3-extension/README.md

@@ -1,10 +1,16 @@
-# @jupyterlab/vega3-extension
+# vega3-extension
 
-A mime-renderer extension for JupyterLab that provides support for rendering Vega and Vega-Lite documents and mimebundles.
+A JupyterLab extension for rendering Vega and Vega-Lite
 
+![demo](http://g.recordit.co/USoTkuCOfR.gif)
 
-Example in Python:
+## Prerequisites
 
+* JupyterLab ^0.27.0
+
+## Usage
+
+To render Vega-Lite output in IPython:
 
 ```python
 from IPython.display import display
@@ -28,3 +34,74 @@ display({
     }
 }, raw=True)
 ```
+
+Using the [altair library](https://github.com/altair-viz/altair):
+
+```python
+import altair as alt
+
+cars = alt.load_dataset('cars')
+
+chart = alt.Chart(cars).mark_point().encode(
+    x='Horsepower',
+    y='Miles_per_Gallon',
+    color='Origin',
+)
+
+chart
+```
+
+Provide vega-embed options via metadata: 
+
+```python
+from IPython.display import display
+
+display({
+    "application/vnd.vegalite.v2+json": {
+        "$schema": "https://vega.github.io/schema/vega-lite/v2.json",
+        "description": "A simple bar chart with embedded data.",
+        "data": {
+            "values": [
+                {"a": "A", "b": 28}, {"a": "B", "b": 55}, {"a": "C", "b": 43},
+                {"a": "D", "b": 91}, {"a": "E", "b": 81}, {"a": "F", "b": 53},
+                {"a": "G", "b": 19}, {"a": "H", "b": 87}, {"a": "I", "b": 52}
+            ]
+        },
+        "mark": "bar",
+        "encoding": {
+            "x": {"field": "a", "type": "ordinal"},
+            "y": {"field": "b", "type": "quantitative"}
+        }
+    }
+}, metadata={
+    "application/vnd.vegalite.v2+json": {
+        "embed_options": {
+            "actions": False
+        }
+    }
+}, raw=True)
+```
+
+Provide vega-embed options via altair:
+
+```python
+import altair as alt
+
+alt.renderers.enable('default', embed_options={'actions': False})
+
+cars = alt.load_dataset('cars')
+
+chart = alt.Chart(cars).mark_point().encode(
+    x='Horsepower',
+    y='Miles_per_Gallon',
+    color='Origin',
+)
+
+chart
+```
+
+To render a `.vl`, `.vg`, `vl.json` or `.vg.json` file, simply open it:
+
+## Development
+
+See the [JupyterLab Contributor Documentation](https://github.com/jupyterlab/jupyterlab/blob/master/CONTRIBUTING.md).