Rewrite of the Introduction documentation

1. Re-aligns the introduction with the new product positioning.
2. Cleanup of some issues with language and formatting.
3. Makes the introduction leaner and meaner.
4. Responds to feedback from product.

Docker-DCO-1.1-Signed-off-by: James Turnbull <james@lovedthanlost.net> (github: jamtur01)
Merge pull request #5897 from jamtur01/newintro

Rewrite of the Introduction documentation