title: Gatsby Images in different folder to markdown
body: <p>I've got an issue trying to reference images that are not in my md folder with AllMarkdownRemark. I've tried and failed to find solutions, including:</p>
  
  <ol>
  <li>Using relative paths</li>
  <li>Using string syntax</li>
  <li>Trying to create an alternative source with the file-system plugin</li>
  </ol>
  
  <p>In my src folder I have a md folder containing markdown files, and an images folder containing the images. The head of an md file looks like this:</p>
  
  <pre><code>---
  path: "/blog/2018"
  date: "2018-11-07"
  title: "My first blog post - THIS IS A TEST!"
  image: "../images/space2.jpg"
  --
  </code></pre>
  
  <p>My graphql query on the blog page looks like this:</p>
  
  <pre><code>query {
    allMarkdownRemark(sort: { fields: [frontmatter___date], order: DESC}) {
      totalCount
      edges {
        node {
          id
          html
          frontmatter {
            title
            path
            date(formatString: "dddd, MMMM Do YYYY")
            image {
                  childImageSharp {
                  fluid(maxWidth: 1440) {
                  ...GatsbyImageSharpFluid
                  }
            }
  
         }
          }
        }
      }
    }
  </code></pre>
  
  <p>This is returning a string because the images folder can't be found by allmarkdownremark. But I have this in my gatsby-config, meaning it should work:</p>
  
  <pre><code>{
          resolve: `gatsby-source-filesystem`,
          options: {
              path: `${__dirname}/src/md/`,
              name: "markdown-pages"
          },
      },
      {
          resolve: `gatsby-source-filesystem`,
          options: {
              path: `${__dirname}/src/images/`,
              name: "images"
          },
      },
  </code></pre>
  
  <p>I'd really appreciate it if anyone could point me in the right direction. </p>