chore(fonts): document

packages/astro/src/assets/fonts/README.md

@@ -1,11 +1,20 @@
 # fonts
 
-The vite plugin orchestrates the fonts logic:
+Here is an overview of the architecture of the fonts in Astro:
 
-- Retrieves data from the config
-- Initializes font providers
-- Fetches fonts data
-- In dev, serves a middleware that dynamically loads and caches fonts data
-- In build, download fonts data (from cache if possible)
-
-The `<Font />` component is the only aspect not managed in the vite plugin, since it's exported from `astro:assets`.
+- [`orchestrate()`](./orchestrate.ts) combines sub steps and takes care of getting useful data from the config
+  - It resolves font families (eg. import remote font providers)
+  - It prepares [`unifont`](https://github.com/unjs/unifont) providers
+  - It initializes `unifont`
+  - For each family, it resolves fonts data and normalizes them
+  - For each family, optimized fallbacks (and related CSS) are generated if applicable
+  - It returns the data
+- [`/logic`](./logic/) contains the sub steps of `orchestrate()` so they can be easily tested
+- The logic uses [inversion of control](https://en.wikipedia.org/wiki/Inversion_of_control) to make it easily testable and swappable
+  - [`definitions.ts`](./definitions.ts) defines dependencies
+  - Those dependencies are implemented in [`/implementations`](./implementations/)
+- [`fontsPlugin()`](./vite-plugin-fonts.ts) calls `orchestrate()` and using its result, setups anything required so that fonts can
+  - Be exposed to users (virual module)
+  - Be used in dev (middleware)
+  - Be used in build (copy)
+- [`<Font />`](../../../components/Font.astro) is managed in [`assets()`](../vite-plugin-assets.ts) so it can be imported from `astro:assets` and consumes the virtual module