Clarify debug docs for deprecated Workload APIs

[briandealwis]

Minor doc modification to expand on debug not handling deprecated workload objects.

[codecov]

Codecov Report

Merging #3092 into master will decrease coverage by 0.03%.
The diff coverage is n/a.

Impacted Files	Coverage Δ
pkg/skaffold/build/local/custom.go	13.33% <0%> (-6.67%)	⬇️
cmd/skaffold/app/cmd/cmd.go	66.92% <0%> (-1.08%)	⬇️
pkg/skaffold/runner/deploy.go	66.66% <0%> (ø)	⬆️
cmd/skaffold/app/cmd/flags.go	100% <0%> (ø)	⬆️
pkg/skaffold/config/options.go	100% <0%> (ø)	⬆️
pkg/skaffold/runner/build_deploy.go	67.18% <0%> (+0.99%)	⬆️
pkg/skaffold/deploy/status_check.go	55.75% <0%> (+1.97%)	⬆️

[container-tools-bot]

Please visit http://35.236.79.92:1313 to view changes to the docs.

The rendered docs looks off http://35.236.79.92:1313/docs/workflows/debug/

[briandealwis]

Unsure why but {{% alert %}} doesn't seem to render the content as markdown. Moved this warning into the Limitations section. Which is where it really belonged.

[container-tools-bot]

Please visit http://35.236.1.119:1313 to view changes to the docs.