Include a hint where to find documentation for DevTools in docs overview

[odrotbohm]

If you look for documentation on the DevTools and arrive at the documentation home page there's no way to find the right sub-section to proceed to. Turn's out it's in "Using Spring Boot". Does it make sense to list DevTools in the summary line? It seems to be a prominent thing to look for in the overview as it's such a distinguished feature.

[wilkinsona]

Done. Thanks for the suggestion, @odrotbohm.