title: Gatsby's Graphql say "Cannot query field "allMarkdownRemark" on type "Query"" and don't appear gatsby-transformer-remark
body: <p>I install gatsby plugin on gatsby template with check gatsby public(<a href="https://www.gatsbyjs.org/packages/gatsby-transformer-remark/" rel="nofollow noreferrer">https://www.gatsbyjs.org/packages/gatsby-transformer-remark/</a>). But the query don't appear to localhost:8000/___graphql.</p>
  
  <p>I build gatsby-site to use <code>gatsby new [name]</code></p>
  
  <p>And install markdown plugin by <code>npm install --save gatsby-transformer-remark</code></p>
  
  <p>And add below line to <code>gatsby-config.js</code>.</p>
  
  <pre><code>plugins: [
    `gatsby-transformer-remark`,
  ]
  </code></pre>
  
  <p>I access to <code>localhost:8000/___graphql</code>.
  But query isn't exist. Graphiql say <strong>"Cannot query field "allMarkdownRemark" on type "Query"."</strong></p>
  
  <p>I do delete cookie, change browser, restart PC, rebuild site, try to install other plugins.
  But don't fix.</p>
  
  <p>Anyone has solution? Please help me!</p>