doc: Fix an unreadable register name hiding behind the border (chap 2.10.2)

[poeschel]

In chapter 2.10.2 there was a bullet list with many register names in uppercase letters on one line. The line rendered to pdf hides some important part of a name of a register out of the page. The proposed fix is a forced newline. This looks ugly, but is at least readable. I'll attach screenshots of the relevant part before:

and after the fix: