Adds a section for the DefinitelyTyped docs

packages/handbook-v1/en/definitely typed/DT Introduction.md

@@ -0,0 +1,12 @@
+---
+title: Introduction to Definitely Typed
+layout: docs
+permalink: /docs/definitely-typed/dt-introduction.html
+oneline: "How to write a definition file for DT."
+wip: true
+---
+
+## Before You Start
+
+If you'd like to learn how to write a high quality type definition (`.d.ts` file) then first run through the [Declaration Files](/docs/handbook/declaration-files/introduction.html).
+These guides are specific to how Definitely Typed works and not about how to write a great definition file.

packages/handbook-v1/en/definitely typed/Testing DT Changes Locally.md

@@ -0,0 +1,18 @@
+---
+title: Try DT Changes Locally
+layout: docs
+permalink: /docs/definitely-typed/testing-locally.html
+oneline: "How to make changes to a DT definition file in your project"
+wip: true
+---
+
+Before you
+
+## Declaration Merging
+
+If the file you want to extend include `interfaces`, then you can include an ambient
+
+```ts
+```
+
+## Patch Package

packages/typescriptlang-org/src/lib/oldHandbookNavigation.ts

@@ -136,6 +136,13 @@ export const oldHandbookNavigation: NavItem[] = [
       { id: "consumption", title: "Consumption" },
     ],
   },
+  {
+    title: "Definitely Typed",
+    id: "definitely-typed",
+    directory: "handbook/definitely-typed",
+    index: "dt-introduction",
+    items: [{ id: "dt-introduction", title: "Introduction" }],
+  },
   {
     title: "Project Configuration",
     id: "project-config",

packages/typescriptlang-org/src/templates/handbook.tsx

@@ -150,6 +150,7 @@ export const pageQuery = graphql`
         title
         disable_toc
         oneline
+        wip
       }
     }
   }