document count method

docs/photon/api.md

@@ -4,6 +4,7 @@ Photon is a type-safe database client auto-generated based on your [data model d
 
 - [Overview](#overview)
 - [CRUD](#crud)
+- [Aggregations](#aggregations)
 - [Field selection](#field-selection)
 - [Relations](#relations)
 - [Raw databases access](#raw-database-access)
@@ -79,6 +80,19 @@ async function main() {
 
 Note that the name of the `users` property is auto-generated using the [`pluralize`](https://github.com/blakeembrey/pluralize) package.
 
+## Aggregations
+
+In addition to CRUD operations, Photon.js also allows for [_aggregation_ queries](https://github.com/prisma/photonjs/issues/5). 
+
+### `count`
+
+To return the number of elements in a list, you can the `count()` method on any model property on your `Photon` instance, for example:
+
+```ts
+const userCount = await photon.users.count()
+// userCount = 42
+```
+
 ## Field selection
 
 This section explains how to predict and control which fields of a model are returned in a Photon API call.
@@ -360,6 +374,21 @@ const deletedUserCount = await photon.users.deleteMany({
 })
 ```
 
+### `count`
+
+Returns the number of elements in a list as a value of type `number`.
+
+#### Options
+
+The `count()` method doesn't take any input arguments.
+
+#### Examples
+
+```ts
+const userCount = await photon.users.count()
+// userCount = 42
+```
+
 ## Filtering
 
 The Photon.js API offers filtering options for constraining the items that are returned from API calls that return lists via the `where` argument.