added API augmentation section

docs/api.adoc

@@ -236,6 +236,77 @@ image::morgan-original.png["The original version of Morgan Freemans photo is wid
 
 NOTE: The red "autofocus" circle, when set, helps the image service to crop the images optimally - as you can see above.
 
-== One final step
+== API augmentation
 
-Knowing how headless a CMS can get with an API calle Guillotine, and GraphQL queries flowing from your fingertips. It's time for the big finale where you <<deploy#, deploy your app to the Enonic cloud>>.
+Now the real magic begins! You programmatically augment and extend the Guillotine API. The use-cases are limitless, but rather than babbling about it - why not try it out yourself?
+
+We'll keep it simple. In the next steps you'll add a new `age` field to the Person content type, and use the `dateofbirth` to calculate the persons age.
+
+. From the `samples/` folder of your app, *copy or move* the `guillotine/` folder to `src/main/resources/`. You should then have the following TypeScript controller ready:
++
+./src/main/resources/guillotine/guillotine.ts
+[source,TypeScript]
+----
+include::{sourcedir}/samples/guillotine/guillotine.ts[]
+----
++
+. Guillotine requires the app to be redeployed (or restarted) in order to pick up changes to schemas and/or controllers. Stop the build (using control-c) and start it again:
++
+  ^c
+  enonic dev
++
+. Back in Query Playground, run the following query: 
++
+.Query using the new field
+[source,GraphQL]
+----
+{
+  guillotine {
+    getChildren(key: "/persons", first: 2) {
+      displayName
+      ... on com_example_myapp_Person {
+        data {
+          age
+          dateofbirth
+        }
+      }
+    }
+  }
+}
+----
++
+The response should now contain a new age filed, with a calculated value:
++
+.Query response
+[source,JSON]
+----
+{
+  "data": {
+    "guillotine": {
+      "getChildren": [
+        {
+          "displayName": "Léa Seydoux",
+          "data": {
+            "age": 38,
+            "dateofbirth": "1985-07-01"
+          }
+        },
+        {
+          "displayName": "Jeffrey Wright",
+          "data": {
+            "age": 58,
+            "dateofbirth": "1965-12-07"
+          }
+        }
+      ]
+    }
+  }
+}
+----
+
+
+As you have now seen, XP lets you run server-side https://developer.enonic.com/docs/xp/stable/framework[TypeScript and JavaScript code]. API augmentation is just the tip of the iceberg - believe us.
+
+== One last thing
+
+With GraphQL queries flowing from your fingertips. It's time for the big finale where you <<deploy#, deploy your app to the Enonic cloud>>.

docs/app.adoc

@@ -67,18 +67,17 @@ Assuming `mysandbox` is still running in another Terminal window, run these comm
   cd myapp
   enonic dev
 
-The last command will build and deploy the app to `mysandbox` - then keep watching for changes in the code to automatically rebuild as you work on it.
+The last command will build and deploy the app to `mysandbox`.
 
 [NOTE]
-====
-Look for the following output to verify that the app has been built:
+===
+The initial build may take a while to setup, look for these lines to confirm it has completed
 
-    BUILD SUCCESSFUL in 6s
-    3 actionable tasks: 3 executed
-    Waiting for changes to input files...
+BUILD SUCCESSFUL in 6s
+3 actionable tasks: 3 executed
+Waiting for changes to input files...
 ====
 
-
 == Moving forward
 
 You just created and built your very own application. In the next chapter you'll get familiar with <<cms#, Content Studio and content modelling>>.

samples/guillotine/guillotine.ts

@@ -0,0 +1,38 @@
+// Using the Person data type
+const personType = 'com_example_myapp_Person_Data';
+
+export const extensions = (graphQL) => {
+	return {
+		creationCallbacks: {
+			[personType]: function (params) {
+				// Add a new field: age
+				params.addFields({
+					age: {
+						type: graphQL.GraphQLInt
+					}
+				});
+			}
+		},
+		resolvers: {
+			[personType]: {
+				// Implement the age resolver
+				age: (env) => {
+                    if (!env.source.dateofbirth) {return null;}
+
+					// Caclulate age
+                    let age = null;
+                	const today = new Date();
+                    const birthDate = new Date(env.source.dateofbirth);
+                    age = today.getFullYear() - birthDate.getFullYear();
+                    const m = today.getMonth() - birthDate.getMonth();
+
+                    // Tune for moth and day
+                    if (m < 0 || (m === 0 && today.getDate() < birthDate.getDate())) {
+                        age--;
+                    }
+                    return age;
+                }
+			}
+		},
+	}
+};