archlinux installation doc: correct some details

1. The AUR package is called docker-git, not lxc-docker-git.

2. According to the official community package, docker depends on
   sqlite.

3. 02ef8ec (Update archlinux.rst as packages have changed, 2013-12-06)
   updated the installation instructions, but left behind residual
   wording about the AUR package not being officially supported; the
   community repository is officially supported.

Signed-off-by: Ramkumar Ramachandra <artagnon@gmail.com>
Added section on Trusted Builds
Make it extra clear that the `docker` group is root-equivalent.
Merge pull request #3143 from idupree/patch-1

Make it extra clear that the `docker` group is root-equivalent.
Merge pull request #3104 from jamtur01/uses

Added section on Trusted Builds
Merge pull request #3109 from artagnon/arch-install

Update Arch installation doc