Adds vendor distro docs
What:
- Adds a new document for vendors who wish to test their distribution with the umbrella package.
- Fixes some spelling errors and adds a link to the new vendordistro.md to the testing.md
Story Link:bb-693
UNCLASSIFIED - NO CUI
Currently supported Big Bang Version is 2.27.0
What:
Story Link:bb-693
UNCLASSIFIED - NO CUI