Provide downloads page

[rgbkrk]

We should make a downloads page with builds of what's on master for people to consume (we also have branches and some commits but I digress).

Update: Installation/configuration instructions are now on ReadTheDocs.

[rgbkrk]

Since we're not providing "installers", you'll have to modify the executable bits on *nix to run these.

17:16:21 rgbkrk@puter ~$ chmod u+x rack-darwin-amd64
17:16:31 rgbkrk@puter ~$ ./rack-darwin-amd64
NAME:
   rack - An opinionated CLI for the Rackspace cloud

USAGE:
   rack [global options] command [command options] [arguments...]

VERSION:
   0.0.0

COMMANDS:
   servers  Used for the Servers service
   help, h  Shows a list of commands or help for one command

GLOBAL OPTIONS:
   --help, -h           show help
   --generate-bash-completion
   --version, -v        print the version

Not sure what Windows needs...

[rgbkrk]

If people need builds for other systems (FreeBSD, 32-bit, ARM), let us know.

Now I realize that if we had ARM support out of the box, people could run this on the raspberry pi...

[rgbkrk]

Welp, now we have ARMs.

[rgbkrk]

Now that the ReadTheDocs page is up and tied into CI/CD, I'd say this is good. To keep us from having to update this issue list with official download/install/usage steps, I'll link it above instead.