Update Python linting docs w/ info on linting on change

[marnovo]

Update Python linting docs w/ info on linting on change:

Target file/documentation: docs/python/linting.md

Based on: microsoft/vscode-python#1231
which implements: microsoft/vscode-python#408

[kraigb]

@DonJayamanne @brettcannon @MikhailArkhipov Can one of you confirm that the Python extension supports python.linting.lintOnTextChange now? I didn't see a doc issue for it before, the setting does appear now in the current release.

[brettcannon]

This is only for the experimental analysis engine, so this is not something to document yet.

[kraigb]

@marnovo With Brett's response, I'm closing this issue because the lint-on-change capability isn't officially supported yet. When it is, we'll be creating a suitable issue here aligned with the release of the extension that contains it, so in the meantime we won't maintain this present issue on a backlog.

[marnovo]

Thanks for the clarification, @kraigb & @brettcannon.

Looking forward to the official release of the analysis engine, particularly this feature.