I am 100% happy for there to be a guide on Meta about how to change branches. I just do not think it belongs in the official install guide, where 95% of people do not care or need to care.
If Basic Bob is trying to install Discourse, he just wants to get through the installation as quickly and easily as possible, so he can work on his new site. Information about changing branches is just going to make him think more, and cause confusion.
Advanced Ally, on the other hand, may be interested in understanding how branches work and which is best for her site. But she’s also likely doing more research prior to installing Discourse, not simply running through the installation guide.