Mention go-global-update in the step list in the wiki

[Gelio]

Hey! I appreciate that https://github.com/Gelio/go-global-update was added as a step in topgrade 🎉

I looked over at the step list in the wiki and it looks like go-global-update is missing there. I wanted to add it there myself, but I am not sure I can add a PR against the wiki and not the main repo. I don't know how I could add it there, so I reckon it must be a maintainer that needs to modify the wiki.

Could you mention go-global-update in the step list in the wiki?

This would make users aware it is run, as well as give them point them to the right repository to install the tool in case they want to handle go executable upgrades