docs: more API v2 descriptions (#45)

This adds descriptions for more API v2 endpoints and improves the
existing description.

content/en/docs/Reference/api/v2.md

@@ -16,12 +16,15 @@ This describes general behavior of all API endpoints
 
 - All API responses either have an empty body (only for HTTP 204 responses) or the body consists of only JSON.
 - The `error` key always has a value of type `string`, containing a human readable error message. Those error messages are intended to be passed to the user of the application.
-- All attributes for a resource are always contained in the objects that the API returns.
+- API responses always contain all attributes for an object
 
 ### Changed in v2
 
+- API responses do not all have a `data` or `error` key on the top level. Unsuccessful requests will have a response with an `error` key (this is unchanged to v1). Successful API responses will behave as described below.
 - API responses are either a list of objects (for collection endpoints) or a single object (for resource endpoints).
-- On `POST` endpoints, each object (in the list, if it's a bulk creation endpoint) always has a `data` and an `error` key. If an error ocurred, `error` will contain an error message. If no error occurs, `error` is `null` and `data` contains the created resource.
+- `POST` endpoints now take a **list** of objects to be created, not a singular object. The response will also be a list of objects, where every object has a `data` and an `error` key. If an error ocurred, `error` will contain an error message. If no error occurs, `error` is `null` and `data` contains the created resource.
+- `PATCH` endpoints and `GET` resource endpoints return the resource object (instead of a map containing a key `data` with the resource object as value)
+- `GET` list endpoints return a list of the resource objects (instead of a map containing a key `data` with a list of the resource objects as value)
 
 ## Migrating from v1