Explain debug paint in the inspector UI

[difujia]

Hi guys, it would be much useful if the inspector UI contains explanations about the debug paint (the yellow arrows, blue/grey boxes, etc.). Currently, I can find some info buried here: https://flutter.dev/docs/testing/debugging#visual-debugging However, this is not thorough and not obvious/convenient for new users like me.

Thanks.

[devoncarew]

We should likely describe it in our docs (https://docs.flutter.dev/tools/devtools/inspector), and perhaps in-line in the UI as well (as a tooltip?).