How to add text into a document without a user input field in Sanity.io

// myIntroTextComponent.js
import React from 'react'
import PropTypes from 'prop-types'
import FormField from 'part:@sanity/components/formfields/default'

export default class IntroText extends React.Component {
  static propTypes = {
    type: PropTypes.shape({
      title: PropTypes.string,
      options: PropTypes.shape({
        intro: PropTypes.string.isRequired
      }).isRequired
    }).isRequired
  }

  render() {
    const {type} = this.props
    const {intro} = type.options

    return (
      <FormField label={type.title}>
        {intro}
      </FormField>
    )
  }
}

import MyIntroTextComponent from '../components/myIntroTextComponent'
...
    {
      name: 'hello',
      title: 'Hello!',
      type: 'string',
      inputComponent: MyIntroTextComponent,
      options: {
        intro: 'This is some page, where you can edit something'
      }
    }
...

import {Link} from 'part:@sanity/base/router'