use apollo client in gatsby code example

Example: apollo client install in gatsby

$ npm install gatsby-plugin-apollo @apollo/client

# yarn
$ yarn add gatsby-plugin-apollo @apollo/client

# gatsby-config.js
module.exports = {
  plugins: [
    {
      resolve: 'gatsby-plugin-apollo',
      options: {
        uri: 'https://example.com/graphql'
      }
    }
  ]
};