Remove 1.0.0-alpha4

To fix the build break and continue maintaining docker
tags starting from beta1, removed 1.0.0-alpha4 dockerfile
and fixed readme.

Signed-off-by: Ahmet Alp Balkan <ahmetb@microsoft.com>
Merge pull request #15 from ahmetalpbalkan/remove-alpha4

Remove 1.0.0-alpha4