Document Alongside mode SteamShell runs in either of two modes now, and the wiki described only one. Adds a page for the pair, and threads it through Install, Home, Settings, the tray page and the sidebar. The Install page's product table had two answers where there are now three: Alongside is the one to start with on a machine that is also a PC, rather than XFE, which is for Xbox FSE rather than for caution.