docs: enhance S3 presigned urls

docs/api/s3.md

@@ -171,11 +171,24 @@ When your production service needs to let users upload files to your server, it'
 
 To facilitate this, you can presign URLs for S3 files. This generates a URL with a signature that allows a user to securely upload that specific file to S3, without exposing your credentials or granting them unnecessary access to your bucket.
 
+The default behaviour is to generate a `GET` URL that expires in 24 hours. Bun attempts to infer the content type from the file extension. If inference is not possible, it will default to `application/octet-stream`.
+
 ```ts
 import { s3 } from "bun";
 
 // Generate a presigned URL that expires in 24 hours (default)
-const url = s3.file("my-file.txt").presign({
+const download = s3.presign("my-file.txt"); // GET, text/plain, expires in 24 hours
+
+const upload = s3.presign("my-file", {
+  expiresIn: 3600, // 1 hour
+  method: 'PUT',
+  type: 'application/json', // No extension for inferring, so we can specify the content type to be JSON
+});
+
+// You can call .presign() if on a file reference, but avoid doing so
+// unless you already have a reference (to avoid memory usage).
+const myFile = s3.file("my-file.txt");
+const presignedFile = myFile.presign({
   expiresIn: 3600, // 1 hour
 });
 ```