readme: add api

README.md

@@ -3,3 +3,31 @@
 [![Build Status](https://travis-ci.org/grvcoelho/webhulk.svg?branch=master)](https://travis-ci.org/grvcoelho/webhulk)
 
 :construction: A lightweight API for managing webhooks
+
+## API
+
+### Webhooks
+
+| Attribute | Type | Description |
+| --------- | ---- | ----------- |
+| `name` | *String* | An indentifier for the webhook |
+| `url` | *String* | The url messages will be sent to |
+| `enabled` | *Boolean* | Whether or not it is enabled |
+
+
+### Messages
+
+| Attribute | Type | Description |
+| --------- | ---- | ----------- |
+| `headers` | *JSON* | The HTTP headers that will be sent |
+| `payload` | *JSON* | The payload that will be sent |
+| `signatures` | *String* | An HMAC signature of the message |
+
+### Deliveries
+
+| Attribute | Type | Description |
+| --------- | ---- | ----------- |
+| `status` | *String* | The status of the delivery. One of: `success`, `failed`, `processing` |
+| `latency` | *JSON* | The time between the delivery and the response from the client |
+| `response_status_code` | *String* | The HTTP status code the client respond with |
+| `response_headers` | *JSON* | The HTTP headers the client respond with |