Update update-osx.md

Author: ArekSredzki

docs/update-osx.md

@@ -3,7 +3,13 @@ Electron Release Server provides a backend for the [Squirrel.Mac](https://github
 
 ### Endpoint
 
-The endpoint for **Squirrel.Mac** is `http://download.myapp.com/update/osx/:currentVersion`. The server is smart enough to also match the platform to `darwin`,`darwin_64`,`macos`, and `mac`.
+The endpoint for **Squirrel.Mac** is `https://download.myapp.com/update/:platform/:version[/:channel]`.
+
+Note that `version` is the currently installed version.
+
+The server will accept the platform as `osx`, `darwin`,`darwin_64`,`macos`, and `mac`.
+
+Since the server supports multiple release channels, you can specify the channel when requesting updates. Examples of supported channels are `stable`, `beta`, `alpha`. Each channel includes those above it; `beta` will include `stable` updates.
 
 This url requires different parameters to return a correct version: `version` and `platform`.