Using dark and light mode-specific images in markdown

a. Append fragment to image URL:

![dark](https://til.andrecostalima.pt/dark.png#gh-dark-mode-only)
![light](https://til.andrecostalima.pt/light.png#gh-light-mode-only)

b. Use <picture> HTML element combined with prefers-color-scheme media query:

<picture>
  <source media="(prefers-color-scheme: dark)" srcset="https://til.andrecostalima.pt/dark.png">
  <img src="https://til.andrecostalima.pt/light.png">
</picture>