[SQL][DOCS] Improve table caching section

Author: Michael Armbrust <michael@databricks.com>

Closes #2434 from marmbrus/patch-1 and squashes the following commits:

67215be [Michael Armbrust] [SQL][DOCS] Improve table caching section

(cherry picked from commit cbf983bb4a550ff26756ed7308fb03db42cffcff)
Signed-off-by: Michael Armbrust <michael@databricks.com>