Create version matrix

[Jeffry Hesse]

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• What are you trying to do?
  The current version list on the README is good, but I think it would likely be visually easier for people if we create a version matrix

• What feature or behavior is this required for?
  Mainly just so people can visually scan a little bit better on what version works with what, etc...

Perhaps we can link to release tags, as well.

• How could we solve this issue? (Not knowing is okay!)
  Have fun! Write some markdown! Trace down what versions of the apt plugin work with what version of Nexus Repo, etc...

• Anything else?

[Mike Poindexter]

Seems like this is now integrated into the readme as a nice matrix/table, so closing out