Update MDX document

[yuta-ike]

This PR added about providerImportSource option, which we need to specify in next.config.js to use MDXProvider.

Related mdx documents: https://mdxjs.com/docs/using-mdx/#mdx-provider

To solve this, a context can be used in React, Preact, and Vue. Context provides a way to pass data through the component tree without having to pass props down manually at every level. Set it up like so:

1. Install either @mdx-js/react, @mdx-js/preact, or @mdx-js/vue, depending on what framework you’re using
2. Configure your MDX integration with options.providerImportSource set to that package, so either '@mdx-js/react', '@mdx-js/preact', or '@mdx-js/vue'
3. Import MDXProvider from that package. Use it to wrap your top-most MDX content component and pass it your components instead:

Because my English skills are not high, feel free to improve my sentences.

Bug

• Related issues linked using fixes #number
• Integration tests added
• Errors have helpful link attached, see contributing.md

Feature

• Implements an existing feature request or RFC. Make sure the feature request has been accepted for implementation before opening a PR.
• Related issues linked using fixes #number
• Integration tests added
• Documentation added
• Telemetry added. In case of a feature if it's used or not.
• Errors have helpful link attached, see contributing.md

Documentation / Examples

• Make sure the linting passes by running yarn lint