Docu missing about lack of whitespace support in values file paths

The following discussion from !2 (merged) should be addressed:

• @alossent started a discussion:

  Please document here the limitation that values paths cannot contain whitespaces, as explained in !2 (diffs, comment 3117172)

  Worth including the link to https://superuser.com/a/1142939, which explains how we could include literal double-quotes in the function output, then turn them into arrays before passing the array of arguments to helm upgrade

  Other options include returning one path per line and more complex processing before passing the arguments to helm upgrade

  Probably not worth the effort of implementing, but that important limitation must at least be documented.