Create get-tmate.sh

[MaxPeal]

for easy download and install

Easyinstall (Defaults to ./bin, and inc. sha256 verify the download)

$ curl -fsSL https://github.com/tmate-io/tmate/raw/master/get-tmate.sh -o get-tmate.sh
$ sh get-tmate.sh

[nviennot]

Can you add instructions on the https://github.com/tmate-io/tmate-master/blob/master/lib/tmate_web/templates/sign_up/home.html.eex as well?

[MaxPeal]

@nviennot done with a draft PR tmate-io/tmate-master#25