Merge pull request plotly#2253 from plotly/doc_checklist

documentation PR checklist

Author: nicolaskruchten

.github/pull_request_template.md

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+Please uncomment this block and take a look at this checklist if your PR is making substantial changes to documentation/impacts files in the `doc` directory. Check all that apply to your PR, and leave the rest unchecked to discuss with your reviewer! Not all boxes must be checked for every PR :)
+
+- [ ] I've [seen the `doc/README.md` file](https://github.com/plotly/plotly.py/blob/master/doc/README.md)
+- [ ] This change runs in the current version of Plotly on PyPI and targets the `doc-prod` branch OR it targets the `master` branch
+- [ ] If this PR modifies the first example in a page or adds a new one, it is a `px` example if at all possible
+- [ ] Every new/modified example has a descriptive title and motivating sentence or paragraph
+- [ ] Every new/modified example is independently runnable
+- [ ] Every new/modified example is optimized for short line count	and focuses on the Plotly/visualization-related aspects of the example rather than the computation required to produce the data being visualized
+- [ ] Meaningful/relatable datasets are used for all new examples instead of randomly-generated data where possible
+- [ ] The random seed is set if using randomly-generated data in new/modified examples
+- [ ] New/modified remote datasets are loaded from https://plotly.github.io/datasets and added to https://github.com/plotly/datasets
+- [ ] Large computations are avoided in the new/modified examples in favour of loading remote datasets that represent the output of such computations
+- [ ] Imports are `plotly.graph_objects as go` / `plotly.express as px` / `plotly.io as pio`
+- [ ] Data frames are always called `df`
+- [ ] `fig = <something>` call is high up in each new/modified example (either `px.<something>` or `make_subplots` or `go.Figure`)
+- [ ] Liberal use is made of `fig.add_*` and `fig.update_*` rather than `go.Figure(data=..., layout=...)` in every new/modified example
+- [ ] Specific adders and updaters like `fig.add_shape` and `fig.update_xaxes` are used instead of big `fig.update_layout` calls in every new/modified example
+- [ ] `fig.show()` is at the end of each new/modified example
+- [ ] `plotly.plot()` and `plotly.iplot()` are not used in any new/modified example
+- [ ] Hex codes for colors are not used in any new/modified example in favour of [these nice ones](https://github.com/plotly/plotly.py/issues/2192)
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+-->