Fix Could not parse expression with acorn error

'{}' is interpreted as javascript by mdx, so curly brackets needs
escaping, either via '\{' '\}' or put it in code blocks.

https://mdxjs.com/docs/troubleshooting-mdx/#could-not-parse-expression-with-acorn-error

docs/tutorials/generate-new-code-using-ai.mdx

@@ -11,7 +11,7 @@ Defang supports generating new project outlines using integration with an AI mod
 
 In this tutorial we'll use the following prompt:
 
-A basic service with 2 REST endpoints. The default endpoint will be for health check and should return a JSON object like this: { "status": "OK" }. The /echo endpoint will echo back all request parameters in the response.
+A basic service with 2 REST endpoints. The default endpoint will be for health check and should return a JSON object like this: `{ "status": "OK" }`. The /echo endpoint will echo back all request parameters in the response.
 
 ## Step 1 - Use the CLI generate command
 ```text