Go to https://www.flowdock.com/oauth/applications and create a new application and grab the Application ID and Secret from there.
Create a file config.toml to the root of the project and add the following
lines:
[Flowdock]
ClientId = "<YOUR APP ID>"
ClientSecret = "<YOUR APP SECRET>"
Then just run:
go run main.go
It'll prompt you for the authorization for the first time you run it.
Use go run main.go -d if you want to see a bunch of debug info.