docs/src/templates/Doc.jsx

import React, { Component } from 'react'
import PropTypes from 'prop-types'
import { graphql } from 'gatsby'
import Layout from '../components/Layout'
import Sidebar from '../components/Sidebar'

export default class DocTemplate extends Component {
    static propTypes = {
        data: PropTypes.object.isRequired,
        location: PropTypes.object.isRequired
    }

    render() {
        const { location } = this.props
        const post = this.props.data.markdownRemark
        const { section } = post.fields

        return (
            <Layout location={location}>
                <Sidebar location={location} sidebar={section} />

                <h1>{post.frontmatter.title}</h1>
                <div dangerouslySetInnerHTML={{ __html: post.html }} />
            </Layout>
        )
    }
}

export const pageQuery = graphql`
    query DocBySlug($slug: String!) {
        site {
            siteMetadata {
                title
            }
        }
        markdownRemark(fields: { slug: { eq: $slug } }) {
            id
            excerpt
            html
            frontmatter {
                title
            }
            fields {
                section
            }
        }
    }
`