Updates React Guide with Gatsby config link
Updates React Guide with Gatsby config link

To use Storybook 5.3 or higher with Gatsby, custom configuration is required. This adds a link to [Gatsby's Storybook guide](https://www.gatsbyjs.org/docs/visual-testing-with-storybook/).

Changes adds to:
## Automatic setup 

The following sentence
If you're using [Gatsby](https://www.gatsbyjs.org/), some added config is required - see [Gatsby's Storybook guide](https://www.gatsbyjs.org/docs/visual-testing-with-storybook/).
storybooks/react-storybook,kadirahq/react-storybook,storybooks/storybook,storybooks/react-storybook,storybooks/storybook,storybooks/react-storybook,storybooks/storybook,storybooks/storybook,storybooks/storybook,storybooks/react-storybook,storybooks/storybook,storybooks/storybook,kadirahq/react-storybook