Update README.md

Fix typo in usage example

README.md

@@ -34,7 +34,7 @@ Then, you can use your favorite HTTP client to call the server's `/embedding` en
 curl \
 -X POST \
 -H "Content-Type: application/json" \
--d '{"text": "Hello, world!"}' \
+-d '{"content": "Hello, world!"}' \
 http://localhost:8080/embedding
 ```