Writing gallery examples

An example is a plain Python script in examples/, such as examples/basics/sine_waves.py:

"""Sine waves

Three harmonics of a fundamental wave, and their sum.

More text, with $math$ if needed.
"""

import plotly.graph_objects as go

fig = go.Figure(...)
fig.show()

• The first docstring line is the title, the first paragraph after it the text on the card, and the whole rest the description above the figure (Markdown and math work).
• fig.show() (Plotly) becomes an interactive figure, plt.show() (matplotlib) a PNG. All the figures a script shows end up on its page, in order, and the first one is the thumbnail.
• The script is shown below the figures without its docstring, and can be downloaded whole.
• Subdirectories become headings in the gallery.

npm run gallery -w example/docs -- execute   # run the scripts that changed
npm run dev