Add Gatsby installation instructions

Author: AryanJ-NYC

.docz/app/db.json

@@ -66,6 +66,25 @@
         ]
       }
     },
+    {
+      "key": "src/pages/installation/gatsby.mdx",
+      "value": {
+        "name": "Gatsby",
+        "route": "/installation/gatsby",
+        "menu": "Installation",
+        "id": "564fc0dc9ce695d4d297e27fac07047b",
+        "filepath": "src/pages/installation/gatsby.mdx",
+        "link": "https://github.com/AryanJ-NYC/reactandtypescript.dev/edit/master/src/pages/installation/gatsby.mdx",
+        "slug": "src-pages-installation-gatsby",
+        "headings": [
+          {
+            "slug": "gatsby",
+            "depth": 1,
+            "value": "Gatsby"
+          }
+        ]
+      }
+    },
     {
       "key": "src/pages/installation/create-react-app.mdx",
       "value": {

.docz/app/imports.js

@@ -7,6 +7,10 @@ export const imports = {
     import(
       /* webpackPrefetch: true, webpackChunkName: "src-pages-examples-functional-components" */ 'src/pages/examples/functional-components.mdx'
     ),
+  'src/pages/installation/gatsby.mdx': () =>
+    import(
+      /* webpackPrefetch: true, webpackChunkName: "src-pages-installation-gatsby" */ 'src/pages/installation/gatsby.mdx'
+    ),
   'src/pages/installation/create-react-app.mdx': () =>
     import(
       /* webpackPrefetch: true, webpackChunkName: "src-pages-installation-create-react-app" */ 'src/pages/installation/create-react-app.mdx'

src/pages/installation/gatsby.mdx

@@ -0,0 +1,29 @@
+---
+name: Gatsby
+route: /installation/gatsby
+menu: Installation
+---
+
+# Gatsby
+
+1\. Install [`gatsby-plugin-typescript`](https://www.gatsbyjs.org/packages/gatsby-plugin-typescript/).
+
+```
+npm install gatsby-plugin-typescript
+```
+
+or
+
+```
+yarn add gatsby-plugin-typescript
+```
+
+2\. Add to array of `plugins` in `gatsby-config.js`:
+
+```js
+// gatsby-config.js
+module.exports = {
+  // ...,
+  plugins: [...`gatsby-plugin-typescript`],
+};
+```