update doc - overview image

docs/docs/getting_started/overview.md

@@ -9,6 +9,8 @@ CocoIndex is an ultra-performant real-time data transformation framework for AI,
 
 As a data framework, CocoIndex takes it to the next level on data freshness. **Incremental processing** is one of the core values provided by CocoIndex.
 
+![Incremental Processing](/img/incremental-etl.gif)
+
 ## Programming Model
 CocoIndex follows the idea of [Dataflow programming](https://en.wikipedia.org/wiki/Dataflow_programming) model. Each transformation creates a new field solely based on input fields, without hidden states and value mutation. All data before/after each transformation is observable, with lineage out of the box.