update pandas references

Author: LiamConnors

doc/python/heatmaps.md

@@ -48,7 +48,7 @@ Plotly supports two different types of colored-tile heatmaps:
 
 
 <!-- #region -->
-The `px.imshow()` function can be used to display heatmaps (as well as full-color images, as its name suggests). It accepts both array-like objects like lists of lists and `numpy` or `xarray` arrays, as well as `pandas.DataFrame` objects.
+The `px.imshow()` function can be used to display heatmaps (as well as full-color images, as its name suggests). It accepts both array-like objects like lists of lists and `numpy` or `xarray` arrays, as well as supported [DataFrame objects](/python/px-arguments#supported-dataframes).
 
 
 > For more examples using `px.imshow`, including examples of faceting and animations, as well as full-color image display, see the [the `imshow` documentation page](/python/imshow).

doc/python/px-arguments.md

@@ -128,14 +128,13 @@ The first argument of every `px` function is `data_frame`. If you provide a Data
 - PyArrow
 - Modin
 
-> To use Polars, PyArrow, or Modin with Plotly Express, you'll need to have NumPy installed. You can install it with: `pip install numpy`
+> To use Polars, PyArrow, or Modin with Plotly Express, you'll need to have NumPy installed. You can install it with: `pip install numpy`.
+To use [trendlines](/python/linear-fits/), you'll also need to have pandas installed. 
 
 `px` uses [Narwhals](https://narwhals-dev.github.io/narwhals/) to natively support these DataFrames. Other types of DataFrames that are currently supported by Narwhals may also work with `px`, for example cuDF.
 
 You can also pass DataFrames that are not natively supported, but support the dataframe interchange protocol, or have a `to_pandas()` method.
 
-> Not all `px` functionality is supported natively for non-pandas DataFrames.
-
 ### Example: Using a Pandas DataFrame with `px.bar`
 
 Here, we create a pandas DataFrame, pass it to `px.bar` as its first argument, and then use the `"sepal_length"` column for the x-axis and the `"sepal_width"` for the y-axis.