docs(website): extend usage section

docs/guide/usage.md

@@ -103,11 +103,11 @@ class User {
 }
 ```
 
-As you can see, your `User` model probably looks completly different from the one you have in your codebase.
+As you can see, your `User` model probably looks completely different from the one you have in your codebase.
 One thing to keep an eye on is the `subscriptionTier` property, as it is not simply a string, but only one of the strings defined in the `SubscriptionTier` type (`'free'` or `'basic'` or `'business'`).
 Also, in a real scenario your model should not depend on a type of a third party library (`SexType` in this case).
 
-Let's create our first user factory function.
+Let's create our first user factory function:
 
 ```ts
 import { faker } from '@faker-js/faker';
@@ -120,7 +120,7 @@ function createRandomUser(): User {
     email: faker.internet.email(),
     firstName: faker.name.firstName(),
     lastName: faker.name.lastName(),
-    sex: faker.name.sexType();
+    sex: faker.name.sexType(),
     subscriptionTier: faker.helpers.arrayElement([
       'free',
       'basic',
@@ -131,3 +131,89 @@ function createRandomUser(): User {
 
 const user = createRandomUser();
 ```
+
+At this point we have a perfectly working function that will work for most purposes.
+But we can take this a step further.
+Currently all properties are just randomly generated.
+This can lead to some undesirable values being produces.
+For example: The `sex` property having value `'female'` while `firstName` is `'Bob'`.
+
+Lets refactor our current code:
+
+```ts {4-7,13-16}
+import { faker } from '@faker-js/faker';
+
+function createRandomUser(): User {
+  const sex = this.faker.name.sexType();
+  const firstName = faker.name.firstName(sex);
+  const lastName = faker.name.lastName();
+  const email = faker.internet.email(firstName, lastName)
+
+  return {
+    _id: faker.datatype.uuid(),
+    avatar: faker.image.avatar(),
+    birthday: faker.date.birthdate(),
+    email,
+    firstName,
+    lastName,
+    sex,
+    subscriptionTier: faker.helpers.arrayElement([
+      'free',
+      'basic',
+      'business',
+    ]),
+  };
+}
+
+const user = createRandomUser();
+```
+
+As you can see, we changed the order in which we generate our values.
+First we generate a `sex` value to use it as input for the generation of `firstName`.
+Then we generate the `lastName`.
+Here, we could also pass in the `sex` value as argument, but in our use-case there are no special cases in where a female last name would differ from a male one.
+By doing this first we are able to pass both names into the `email` generation function.
+This allows the value to be more reasonable based on the provided arguments.
+
+But we can take this even another step further.
+Opposite to the `_id` property that uses an `uuid` implementation, which is unique by design, the `email` property potentially isn't.
+But in most use-cases this would be desireable.
+
+Faker got your back, with another helper method:
+```ts {7-9}
+import { faker } from '@faker-js/faker';
+
+function createRandomUser(): User {
+  const sex = this.faker.name.sexType();
+  const firstName = faker.name.firstName(sex);
+  const lastName = faker.name.lastName();
+  const email = faker.helpers.unique(
+    faker.internet.email,
+    [
+      firstName, 
+      lastName,
+    ],
+  );
+
+  return {
+    _id: faker.datatype.uuid(),
+    avatar: faker.image.avatar(),
+    birthday: faker.date.birthdate(),
+    email,
+    firstName,
+    lastName,
+    sex,
+    subscriptionTier: faker.helpers.arrayElement([
+      'free',
+      'basic',
+      'business',
+    ]),
+  };
+}
+
+const user = createRandomUser();
+```
+
+By wrapping Faker's `email` function with the [`unique`](../api/helpers.md#unique) helper function we ensure that the return value of `email` is always unique.
+
+Congratulation, you should now be able to create any complex object you desire. Happy faking 🥳.