I want to try (in the future), but the way I have Seaside in my images, it is loaded from StHub, so I have no GitHub repos. 

Is there a place/document that describes the procedure of how to do it the recommended way ? And a description of how the releases are structured ?

I started writing that last year: https://github.com/SeasideSt/Seaside/wiki/Contributing
Since Pharo 6 has Iceberg now, I think it���s a good time to make the real switch.

Last year, Philippe made all changes to the develop branch at the ESUG sprint. 

I dropped the ball on Seaside last year and did not produce any updated configuration or anything. 
Trying to pick it up right now and hoping others will follow the model ;)

Johan