Development docs warning for beta-docs.docker.io

Update: Fix alignment issues of the "warning" block.

Docker-DCO-1.1-Signed-off-by: O.S. Tezer <ostezer@gmail.com> (github: ostezer)

Docker-DCO-1.1-Signed-off-by: O.S.Tezer <ostezer@gmail.com> (github: SvenDowideit)
make the non-release doc warning conditional and add version info

use the beta-warning area to tell the user what VERSION of docker, git
branch, and links to the official release version docs are.

requires / extends PR #5272

Docker-DCO-1.1-Signed-off-by: Sven Dowideit <SvenDowideit@fosiki.com> (github: SvenDowideit)
Merge pull request #5351 from SvenDowideit/docs-conditional-beta-warning

Docs conditional beta warning