Arch Linux doesnt have a plan of proper handling the documentation provided by upstream projects.
It has been 2 years since JGC had said:
"Our policy for documentation is a bit weird at this moment. Take a look in /usr/share/doc -> you'll find directories named after the package name, directories with capitals in it, directories with versions, etc. Another thing is the name of the copyright file in /usr/share/licenses/$pkgname. If we want to change this, we should take some steps:..." on https://bugs.archlinux.org/task/12688#comment37047 yet very little has being done towards that direction.

Obviously Arch has come a long way.
From the "man pages all the way" moto, to including and handling info files and of course not stripping out the documentation which is being built by the packages by default.
But the truth is, you cant rely on upstream to build and install all the useful documentation part of their sources. In many occasions example configuration files, example usage files and many other immensly helpful and valuable resources that accompany the sources Arch Linux distributes are unavailable in the package due to this lack of plan and users are forced to download the upstream sources themselves to read them. Unlike eg. man pages, those resources are not available anywhere else.

I would like to request for packages to get built with such useful documentation included.
The documentation that gets built by default is rarely useful. COPYING and AUTHORS files is documentation hardly anyone needs to consult.
Obviously what gets in the package will be pretty much up to its maintainer and probably will require manual intervention and judgement on what to include and what not.
It is my firm belief though, that improving the situation with documentation will benefit the Arch Linux in numerous ways.