use serde::{Serialize, Deserialize};
...
impl Store {
    fn new() -> Self {
        Store {
            questions: Self::init(),
        }
    }

    fn init() -> HashMap<QuestionId, Question> {
        let file = include_str!("../questions.json");
        serde_json::from_str(file).expect("can't read questions.json")
    }
    fn add_question(mut self, question: Question) -> Self {
        self.questions.insert(question.id.clone(), question);
        self
    }

}