Introduction should clarify that hashes are used in paths to software

[tejing1]

This section:

nix-book/src/ch02-00-introduction.md

Lines 12 to 18 in f6448f4

	This information is aggregated through hashing, and allows nix to
	describe and reference the exact software which is intended to use.
	This enables nix to be used on any system because it's assumptions
	do not collide with the assumptions of a host system. This also means that
	nix does not adhere to the traditional [File Hierarchical System(FHS)](https://en.wikipedia.org/wiki/Filesystem_Hierarchy_Standard)
	but it also means that it's not limited to FHS's restriction of only having
	a single variant of a piece of software.

is difficult to follow because no mention has yet been made that hashes are used to determine the paths at which software is installed. Many of the claims in this paragraph don't make sense without that context.

[jonringer]

;( Fair, I'll think about how to word this in a more clear way.

[tejing1]

The first few paragraphs are the hardest to get right, but also the most important. I'm sure it'll take some iterating.

Is it enough to just make it:

This information is aggregated through hashing, and used to determine the software's installation path, allowing nix to describe...