docker: update description
docker: update description

* reword docker officially supported hosts section
* bump minimal required kernel from 3.8 to 3.10

Signed-off-by: Fathi Boudra <7cd6e55cc07a66bc71d7901a4cddfe6c22aab659@linaro.org>
Signed-off-by: Bruce Ashfield <284cc737d174a260eec2a2a6324a304f84b1ae0f@windriver.com>

lgirdk/meta-virtualization,lgirdk/meta-virtualization,cardoe/meta-virtualization,lgirdk/meta-virtualization,cardoe/meta-virtualization,cardoe/meta-virtualization,lgirdk/meta-virtualization,lgirdk/meta-virtualization