docs: updates pet store description location

Signed-off-by: Vincent Biret <[email protected]>

Author: baywet

README.md

@@ -79,7 +79,7 @@ var document = new OpenApiDocument
 Reading and writing an OpenAPI description
 
 ```C#
-var (openApiDocument, _) = await OpenApiDocument.LoadAsync("https://raw.githubusercontent.com/OAI/OpenAPI-Specification/main/examples/v3.0/petstore.yaml");
+var (openApiDocument, _) = await OpenApiDocument.LoadAsync("https://raw.githubusercontent.com/OAI/OpenAPI-Specification/refs/heads/main/_archive_/schemas/v3.0/pass/petstore.yaml");
 
 // Write V2 as JSON
 var outputString = await openApiDocument.SerializeAsJsonAsync(OpenApiSpecVersion.OpenApi2_0);