docs: add pandas to the README Quickstart Plotly Express install command

The Plotly Express quickstart example (px.bar with list inputs) requires
pandas, but the install command only listed plotly[express], which does not
pull in pandas. A fresh environment following the quickstart fails with
'NotImplementedError: Pandas installation is required if no dataframe is
provided.' Add pandas to the install line so the example runs as written.

Author: DawnofGenX

CHANGELOG.md

@@ -8,6 +8,7 @@ This project adheres to [Semantic Versioning](http://semver.org/).
 - Add support for converting matplotlib reference lines (`axhline`, `axvline`, and horizontal/vertical `axline`) as well as axes-coordinate lines into Plotly layout shapes in `mpl_to_plotly`, including support for date axes [[#5719](https://github.com/plotly/plotly.py/pull/5719)], with thanks to @robertoffmoura for the contribution!
 
 ### Fixed
+- Fix the README Quickstart: the Plotly Express example requires pandas, so its install command now includes it
 - Fix `mpl_to_plotly` tick marker mirroring, axis positioning, and trace visibility for twinned and overlaid subplots (such as `twinx` and `twiny`) [[#5310](https://github.com/plotly/plotly.py/pull/5310)], with thanks to @robertoffmoura for the contribution!
 - Fix `mpl_to_plotly` losing matplotlib axis line colors by exporting the color of each axis's displayed spine to the plotly x and y axis `linecolor` [[#5311](https://github.com/plotly/plotly.py/pull/5311)], with thanks to @robertoffmoura for the contribution!
 - Fix concurrent first access to lazily initialized graph object properties, which could raise `ValueError("Invalid value")` [[#5691](https://github.com/plotly/plotly.py/pull/5691)], with thanks to @hb1915 for the contribution!

README.md

@@ -55,7 +55,7 @@ fig.show()
 ### Plotly Express
 
 ```
-pip install plotly[express]
+pip install plotly[express] pandas
 ```
 
 ```python