title: Filtering multiple types of content in graphql
body: <p>I am using GatsbyJS and this is my first adventure with react and graphql. I am wanting to mix a single page's content to contain both "blog-post" type content, and "repo-post" type content, but I don't know how to add that to the query to filter for it.</p>
  
  <p>Additionally; I know what frontmatter is (re: markdown), but I don't know what templateKey, and "eq" are in this context. I don't know enough about what I am looking at to know what it's called to start searching for an explanation.</p>
  
  <pre><code>export const pageQuery = graphql`
    query IndexQuery {
      allMarkdownRemark(
        sort: { order: DESC, fields: [frontmatter___date] },
        filter: { frontmatter: { templateKey: { eq: "blog-post" } }}
      ) {
        edges {
          node {
            excerpt(pruneLength: 400)
            id
            fields {
              slug
            }
            frontmatter {
              title
              templateKey
              date(formatString: "MMMM DD, YYYY")
            }
          }
        }
      }
    }
  `
  </code></pre>