documentation pytest with codecoverage reporing

[codecov-commenter]

Codecov Report

Patch and project coverage have no change.

Comparison is base (9b066cb) 97.01% compared to head (31c897e) 97.01%.

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Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #279 +/- ## ======================================= Coverage 97.01% 97.01% ======================================= Files 1 1 Lines 134 134 Branches 17 17 ======================================= Hits 130 130 Misses 1 1 Partials 3 3 ``` Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=helloflask). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=helloflask)

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[greyli]

The coverage report only works on Python files, but our code base is the Jinja template. I think it's not necessary to address this in the docs.

[PanderMusubi]

For future reference, documented at https://github.com/helloflask/bootstrap-flask/discussions/276