Document how to set release channel for github publisher

Author: rotu

pages/tutorials/release-using-channels.md

@@ -33,6 +33,8 @@ If you want to use channels, you should add this to your package.json:
 
 All you have to do to release using channels is to define the channel in the version tag of the `package.json`. Add "-beta" or "-alpha" (nothing for "latest") to automatically build for the related channel.
 
+!!! warning
+    Github release does not respect the version in the version tag even if `detectUpdateChannel` is true. You must *explicitly* set [`channel`](../builder-util-runtime.interface.githuboptions#channel) to match the intended release channel.
 
 ### Your Application
 All you need to do here is to define which channel the user will receive with: