📝 Add Squirrel's server settings in auto-updater doc.

docs/api/browser/auto-updater.md

@@ -1,8 +1,96 @@
 # auto-updater
 
-The `auto-updater` module is a simple wrap around the
-[Squirrel](https://github.com/Squirrel/Squirrel.Mac) framework, you should
-follow Squirrel's instructions on setting the server.
+**This module has only been implemented for Mac OS X.**
+
+The `auto-updater` module is a simple wrap around the `Squirrel` framework, the
+`Squirrel` framework is not open sourced yet and atom-shell would download the
+binary of `Squirrel` when bootstrapping.
+
+## Squirrel
+
+Squirrel is an OS X framework focused on making application updates **as safe
+and transparent as updates to a website**.
+
+Instead of publishing a feed of versions from which your app must select,
+Squirrel updates to the version your server tells it to. This allows you to
+intelligently update your clients based on the request you give to Squirrel.
+
+Your request can include authentication details, custom headers or a request
+body so that your server has the context it needs in order to supply the most
+suitable update.
+
+The update JSON Squirrel requests should be dynamically generated based on
+criteria in the request, and whether an update is required. Squirrel relies
+on server side support for determining whether an update is required, see
+[Server Support](#server-support).
+
+Squirrel's installer is also designed to be fault tolerant, and ensure that any
+updates installed are valid.
+
+## Update Requests
+
+Squirrel is indifferent to the request the client application provides for
+update checking. `Accept: application/json` is added to the request headers
+because Squirrel is responsible for parsing the response.
+
+For the requirements imposed on the responses and the body format of an update
+response see [Server Support](#server-support).
+
+Your update request must *at least* include a version identifier so that the
+server can determine whether an update for this specific version is required. It
+may also include other identifying criteria such as operating system version or
+username, to allow the server to deliver as fine grained an update as you
+would like.
+
+How you include the version identifier or other criteria is specific to the
+server that you are requesting updates from. A common approach is to use query
+parameters, like this:
+
+```javascript
+// On browser side
+var app = require('app');
+var autoUpdater = require('auto-updater');
+autoUpdater.setFeedUrl('http://mycompany.com/myapp/latest?version=' + app.getVersion());
+```
+
+## Server Support
+
+Your server should determine whether an update is required based on the
+[Update Request](#update-requests) your client issues.
+
+If an update is required your server should respond with a status code of
+[200 OK](http://tools.ietf.org/html/rfc2616#section-10.2.1) and include the
+[update JSON](#update-json-format) in the body. Squirrel **will** download and
+install this update, even if the version of the update is the same as the
+currently running version. To save redundantly downloading the same version
+multiple times your server must not inform the client to update.
+
+If no update is required your server must respond with a status code of
+[204 No Content](http://tools.ietf.org/html/rfc2616#section-10.2.5). Squirrel
+will check for an update again at the interval you specify.
+
+## Update JSON Format
+
+When an update is available, Squirrel expects the following schema in response
+to the update request provided:
+
+```json
+{
+  "url": "http://mycompany.com/myapp/releases/myrelease",
+  "name": "My Release Name",
+  "notes": "Theses are some release notes innit",
+  "pub_date": "2013-09-18T12:29:53+01:00",
+}
+```
+
+The only required key is "url", the others are optional.
+
+Squirrel will request "url" with `Accept: application/zip` and only supports
+installing ZIP updates. If future update formats are supported their MIME type
+will be added to the `Accept` header so that your server can return the
+appropriate format.
+
+`pub_date` if present must be formatted according to ISO 8601.
 
 ## Event: checking-for-update