Updating documentation for negative_revalidating_lifetime (#7633)
Updating documentation for negative_revalidating_lifetime (#7633)

This clarifies the documentation for negative_revalidating_lifetime
which has previously proved to be a source of confusion to users.
duke8253/trafficserver,vmamidi/trafficserver,pbchou/trafficserver,bryancall/trafficserver,bryancall/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,vmamidi/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver,vmamidi/trafficserver,pbchou/trafficserver,duke8253/trafficserver,duke8253/trafficserver,pbchou/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,pbchou/trafficserver,pbchou/trafficserver,duke8253/trafficserver,bryancall/trafficserver,duke8253/trafficserver,vmamidi/trafficserver,SolidWallOfCode/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver,bryancall/trafficserver,vmamidi/trafficserver,duke8253/trafficserver,SolidWallOfCode/trafficserver