[AIRFLOW-XXX] Local development environments - polish documentation

[potiuk]

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[efedotova]

I'd like to move the section BREEZE.rst#debugging-airflow-breeze-tests-in-ide to this doc. Do you think it makes sense?

[potiuk]

Yeah. That should be OK. However just thinking maybe we should have a separate TESTING.rst for example that we could describe both - testing with local virtualenv and Breeze? Just a thought - I do not feel strong about it, but I think since we already have few documents, it might make sense ? What do you think? I think you mentioned once that it's better to have one doc rather than many, but maybe in this case this will be justified since we can have links between the docs.

[efedotova]

Let's beef them up first and see whether more granular docs are required. Actually, adding a TOC pane would help to navigate in a bigger doc...

[potiuk]

One thing that we might add here is using pyenv (https://github.com/pyenv/pyenv) and pyenv-virtualenv (https://github.com/pyenv/pyenv-virtualenv) rather than virtualenvrapper (or as another alternative). It seems to be more "modern" and preferred by a number of people.

[potiuk]

Like it !

[potiuk]

Next round of doc fixes by @efedotova (@kaxil @mik-laj )?