Tutorial: clean up typos, grammar and formatting

This set of changes is just minor cleanup. Some points to note after making this cleanup pass:

• The tutorial overall would benefit from a more comprehensive pass to bring more consistency to how code is referred to in the text. I was also surprised that none of the commands, properties or variables seem to cross-reference the relevant docs for those things.

• The last two sections of the tutorial seem to be incomplete. The Import a CMake Project (Consumer) section talks about an example but doesn't go into any detail at all (I initially thought it was missing altogether until I realised it was referring to the Consumer subdirectory). The Packaging Debug and Release (MultiPackage) section mentions a MultiCPackConfig.cmake file that, while present in the MultiPackage subdirectory, is never explained. Those things should ideally be addressed before the final 3.16 release (in a separate MR to this one though).