complete openbis docker ingress container docs

See merge request !34

BIS-999: A fix for the case when an image reference is an absolute URL path. Treating "file:///" URL and others as absolute URLs.

BIS-999: Added extra check for the value "\uFFFD(undefined)". Now we ignore "<p>\uFFFD(undefined)</p>" as well.

BIS-999: Fixing IOException, when a property contains an image tag which does not point to anything.

BIS-999: Fixing IOException, when a property contains an image tag which does not point to anything.