Make category pages work.

app/src/components/sidebar.js

@@ -0,0 +1,38 @@
+import React from "react";
+import { Nav } from "react-bootstrap";
+import { StaticQuery, graphql } from "gatsby"
+import '../styles/sidebar.css'
+
+export default () => {
+    return (
+        <StaticQuery
+            query={graphql`query CategoryQuery {
+                allCategoriesJson {
+                  edges {
+                    node {
+                      id
+                      name
+                    }
+                  }
+                }
+              }
+            `}
+            render={data => (
+                <Nav className="col-md-12 d-none d-md-block bg-light sidebar"
+                    activeKey="/home"
+                    onSelect={selectedKey => alert(`selected ${selectedKey}`)}
+                >
+                    <div className="sidebar-sticky"></div>
+                    {data.allCategoriesJson.edges.map(function (x, index) {
+                        return (
+                            <Nav.Item>
+                                <Nav.Link href="/home">{x.node.name}</Nav.Link>
+                            </Nav.Item>
+                        )
+                    })}
+                </Nav>
+            )}
+        />
+    );
+};
+