add inference graph image

Signed-off-by: Dan Sun <[email protected]>

Author: yuzisun

docs/blog/articles/2022-07-21-KServe-0.9-release.md

@@ -16,6 +16,7 @@ KServe has the unique strength to build the distributed inference graph with its
 **InferenceGraph** is made up of a list of routing nodes with each node consisting of a set of routing steps. Each step can either route to an InferenceService or another node defined on the graph which makes the InferenceGraph highly composable.
 The graph router is deployed behind an HTTP endpoint and can be scaled dynamically based on request volume. The InferenceGraph supports four different types of routing nodes: **Sequence**, **Switch**, **Ensemble**, **Splitter**.
 
+![InferenceGraph](../../modelserving/inference_graph/inference_graph.png)
 
 - **Sequence Node**: It allows users to define multiple `Steps` with `InferenceServices` or `Nodes` as routing targets in a sequence. The `Steps` are executed in sequence and the request/response from the previous step and be passed to the next step as input based on configuration.
 - **Switch Node**: It allows users to define routing conditions and select a `Step` to execute if it matches the condition. The response is returned as soon as it finds the first step that matches the condition. If no condition is matched, the graph returns the original request.