Update S3-CORS.md

S3-CORS.md

@@ -7,12 +7,48 @@ SeaweedFS supports S3-compatible Cross-Origin Resource Sharing (CORS) configurat
 CORS defines a way for web applications running at one domain to access resources at another domain. When a web application tries to access your S3 bucket from a different domain, the browser will first send a preflight OPTIONS request to check if the cross-origin request is allowed.
 
 SeaweedFS handles CORS through:
+- **Global CORS configuration**: Server-wide default CORS settings
 - **Bucket-level CORS configuration**: Each bucket can have its own CORS rules
 - **Persistent storage**: CORS configurations are stored in bucket metadata
 - **Automatic header handling**: CORS middleware automatically applies appropriate headers
 - **Preflight request support**: Proper handling of OPTIONS requests
 
-## CORS Configuration
+## Quick Start: Global CORS Configuration
+
+The simplest way to enable CORS for all buckets is using the `-s3.allowedOrigins` parameter:
+
+```bash
+# Allow all origins (useful for development)
+weed server -s3 -s3.allowedOrigins=*
+
+# Allow specific origins
+weed server -s3 -s3.allowedOrigins=https://app.example.com,https://admin.example.com
+
+# Docker Compose example
+services:
+  seaweedfs:
+    image: chrislusf/seaweedfs:latest
+    command: "server -s3 -s3.allowedOrigins=*"
+```
+
+This global configuration:
+- Works immediately without additional setup
+- Applies to all buckets by default
+- Can be overridden by bucket-level CORS configuration
+- Supports GET, PUT, POST, DELETE, and HEAD methods
+- Allows all headers (*)
+
+### CORS Configuration Priority
+
+SeaweedFS uses the following priority order:
+
+1. **Bucket-level CORS** (if configured via `aws s3api put-bucket-cors`) - highest priority
+2. **Global CORS** (from `-s3.allowedOrigins` parameter) - fallback if no bucket config
+3. **No CORS** (if neither is configured) - no CORS headers applied
+
+This means you can set a permissive global default and override it with stricter rules for specific buckets.
+
+## Advanced: Bucket-Level CORS Configuration
 
 ### Basic CORS Rule Structure