add zero downtime deployments to subnav [#161264646]
add zero downtime deployments to subnav [#161264646]

Signed-off-by: Landon Jarzynski <2ace4cf343633d412c61d4329fdd2b452fb27ea3@pivotal.io>

swisscom/docs-appcloud-book,cloudfoundry/docs-book-cloudfoundry,swisscom/docs-appcloud-book,swisscom/docs-appcloud-book,swisscom/docs-appcloud-book,cloudfoundry/docs-book-cloudfoundry,cloudfoundry/docs-book-cloudfoundry,cloudfoundry/docs-book-cloudfoundry