Update SearchQnA README.md for its workflow (#913)

Signed-off-by: Tsai, Louie <louie.tsai@intel.com>

SearchQnA/README.md

@@ -20,6 +20,71 @@ The workflow falls into the following architecture:
 
 ![architecture](./assets/img/searchqna.png)
 
+The SearchQnA example is implemented using the component-level microservices defined in [GenAIComps](https://github.com/opea-project/GenAIComps). The flow chart below shows the information flow between different microservices for this example.
+
+```mermaid
+---
+config:
+  flowchart:
+    nodeSpacing: 400
+    rankSpacing: 100
+    curve: linear
+  themeVariables:
+    fontSize: 50px
+---
+flowchart LR
+    %% Colors %%
+    classDef blue fill:#ADD8E6,stroke:#ADD8E6,stroke-width:2px,fill-opacity:0.5
+    classDef orange fill:#FBAA60,stroke:#ADD8E6,stroke-width:2px,fill-opacity:0.5
+    classDef orchid fill:#C26DBC,stroke:#ADD8E6,stroke-width:2px,fill-opacity:0.5
+    classDef invisible fill:transparent,stroke:transparent;
+    style SearchQnA-MegaService stroke:#000000
+
+    %% Subgraphs %%
+    subgraph SearchQnA-MegaService["SearchQnA MegaService "]
+        direction LR
+        EM([Embedding MicroService]):::blue
+        RET([Web Retrieval MicroService]):::blue
+        RER([Rerank MicroService]):::blue
+        LLM([LLM MicroService]):::blue
+    end
+    subgraph UserInterface[" User Interface "]
+        direction LR
+        a([User Input Query]):::orchid
+        UI([UI server<br>]):::orchid
+    end
+
+
+
+    TEI_RER{{Reranking service<br>}}
+    TEI_EM{{Embedding service <br>}}
+    VDB{{Vector DB<br><br>}}
+    R_RET{{Web Retriever service <br>}}
+    LLM_gen{{LLM Service <br>}}
+    GW([SearchQnA GateWay<br>]):::orange
+
+    %% Questions interaction
+    direction LR
+    a[User Input Query] --> UI
+    UI --> GW
+    GW <==> SearchQnA-MegaService
+    EM ==> RET
+    RET ==> RER
+    RER ==> LLM
+
+    %% Embedding service flow
+    direction LR
+    EM <-.-> TEI_EM
+    RET <-.-> R_RET
+    RER <-.-> TEI_RER
+    LLM <-.-> LLM_gen
+
+    direction TB
+    %% Vector DB interaction
+    R_RET <-.-> VDB
+
+```
+
 ## Deploy SearchQnA Service
 
 The SearchQnA service can be effortlessly deployed on either Intel Gaudi2 or Intel Xeon Scalable Processors.