docs: add flowchart

README.md

@@ -7,9 +7,54 @@
 The crawler identifies source repositories from registered [PURLs (Package URLs)][purl] and copies VEX documents into VEX Hub.
 This process ensures that VEX Hub maintains an up-to-date collection of VEX documents for various software packages.
 
+The following diagram illustrates the high-level process flow of the VEX Hub Crawler, using npm as an example:
+
+```mermaid
+flowchart TD
+    Dev[Developer] -->|1. Register Package| PL[Package List]
+    PL -->|2. Provide packages for crawling| Crawler
+    Crawler -->|3. Identify repository URL| Registry[Package Registry]
+    Crawler -->|4. Retrieve VEX documents| Src
+    Crawler -->|5. Validate and update VEX documents| Hub
+
+    subgraph crawler [VEX Hub Crawler]
+        Crawler
+        PL
+    end
+
+    subgraph bottom [  ]
+        direction LR
+        Registry
+        Src
+        Hub[VEX Hub]
+
+        subgraph Src[Source Repository]
+            direction TB
+            VEX[VEX documents\nunder .vex/ directory]
+        end
+    end
+
+
+    classDef dev fill:#b3d9ff,stroke:#2a4d69,stroke-width:1px,color:#2a4d69;
+    classDef vexHub fill:#ffd9e6,stroke:#4b3832,stroke-width:1px,color:#4b3832;
+    classDef crawler fill:#c2f0c2,stroke:#1e4d2b,stroke-width:1px,color:#1e4d2b;
+    classDef npmReg fill:#ffe6cc,stroke:#5e3023,stroke-width:1px,color:#5e3023;
+    classDef sourceRepo fill:#e6ccff,stroke:#3b2e58,stroke-width:1px,color:#3b2e58;
+    classDef pkgList fill:#ccf2ff,stroke:#1c4e5a,stroke-width:1px,color:#1c4e5a;
+    classDef invisible fill:none,stroke:none;
+
+    class Dev dev;
+    class Hub vexHub;
+    class crawler crawler;
+    class Registry npmReg;
+    class Src,VEX sourceRepo;
+    class PL pkgList;
+    class bottom invisible;
+```
+
 ## Registering PURLs
 
-VEX Hub maintains [a list of PURLs](./crawler.yaml) for discovering VEX documents.
+VEX Hub Crawler maintains [a list of PURLs](./crawler.yaml) for discovering VEX documents.
 The PURL definition file format is as follows:
 
 ```yaml