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 post = this.props.data.markdownRemark

        return (
            <Layout location={this.props.location}>
                <Sidebar
                    location={this.props.location}
                    sidebar={post.frontmatter.sidebar}
                />

                <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
                sidebar
            }
        }
    }
`