Update and add documentation to say we now require 3.8.0

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Merge pull request #4 from SvenDowideit/error_out_kernel_req-docs

Update and add documentation to say we now require 3.8.0