[router] add basic usage doc (sgl-project#8640)

Author: slin1237

sgl-router/README.md

@@ -54,12 +54,35 @@ pip install -e .
 ```bash
 # Build Rust components
 cargo build
+```
 
+#### Launch Router with Worker URLs in regular mode
+```bash
 # Launch router with worker URLs
 python -m sglang_router.launch_router \
     --worker-urls http://worker1:8000 http://worker2:8000
 ```
 
+#### Launch Router with Worker URLs in prefill-decode mode
+```bash
+# Note that the prefill and decode URLs must be provided in the following format:
+# http://<ip>:<port> for  decode nodes
+# http://<ip>:<port> bootstrap-port for  prefill nodes, where bootstrap-port is optional
+# Launch router with worker URLs
+python -m sglang_router.launch_router \
+    --pd-disaggregation \
+    --policy cache_aware \
+    --prefill http://127.0.0.1:30001 9001 \
+    --prefill http://127.0.0.2:30002 9002 \
+    --prefill http://127.0.0.3:30003 9003 \
+    --prefill http://127.0.0.4:30004 9004 \
+    --decode http://127.0.0.5:30005 \
+    --decode http://127.0.0.6:30006 \
+    --decode http://127.0.0.7:30007 \
+    --host 0.0.0.0 \
+    --port 8080
+````
+
 ## Configuration
 
 ### Logging