Add an HTML form in thread posting page to send an email when posting

Hi there,

Firstly, thank you so much for this highly valuable software. I love the Misago project and I want to use it for several personal and professional projects I have.

However, even though I am a data scientist (python, R), I am quite new to this kind of web development and I need help with the basics now.

I am using the docker image here.
Actually, I want to modify a bit some HTML pages like in how-to-change-the-thread-template or need-help-for-front-end-customization.
It seems that these topics are not relevant anymore for this version of Misago (v4).
I wish to add another text case in the thread posting page to ask an email address which receives a notification when the topic is posted.

To start, I was aiming at only the page design, to look at later on the email sending process.
To do so, I tried to modify the frontend/src/components/posting/start.js and start-private.js files (adding a <div> with new text) without success following the 'docker-compose up' commands.

Could you give me some advices or information to figure it out, please?

Thanks!

A piece of my code in start.js file:

<Container className="posting-form" withFirstRow={true}>
        <form onSubmit={this.handleSubmit}>
          <div className="row first-row">
            <div className="col-xs-12">
              <input
                className="form-control"
                disabled={this.state.isLoading}
                onChange={this.onToChange}
                placeholder={gettext(
                  "Comma separated list of user names, eg.: Danny, Lisa"
                )}
                type="text"
                value={this.state.to}
              />
            </div>
          </div>
          <div className="row first-row">
            <div className="col-xs-12">
              <input
                className="form-control"
                disabled={this.state.isLoading}
                onChange={this.onEmailChange}
                placeholder={gettext(
                  "Comma separated list of email to reach out"
                )}
                type="text"
                value={this.state.to}
              />
            </div>
          </div>
          ...