Get an extra pair of eyes on the Softlayer installation docs

Docker-DCO-1.1-Signed-off-by: SvenDowideit <SvenDowideit@home.org.au> (github: SvenDowideit)
Merge pull request #7152 from SvenDowideit/get-help-maintaining-softlayer-docs

MAINTAINERS: Get an extra pair of eyes on the Softlayer installation docs