Added some explanations for various crates.

Signed-off-by: Narfinger <[email protected]>

Author: Narfinger

src/SUMMARY.md

@@ -31,6 +31,7 @@
 
 # Servo’s architecture
 
+- [Crates under Servo\*](architecture/crates.md)
 - [Architecture overview\*](architecture/overview.md)
   - [Concurrency and parallelism\*](architecture/concurrency-and-parallelism.md)
   - [Further reading\*](architecture/further-reading.md)

src/architecture/crates.md

@@ -0,0 +1,23 @@
+# Architecture overview
+
+The servo browser owns a couple of crates that are either mostly independent or based on some upstream project. This gives a list of them.
+We highlight crates with **crate** for crates that are used throughout the rust ecosystem and _crate_ for crates used in Firefox work.
+You should use a bit more care before changing them.
+
+- servo: The main browser
+- _mozjs_: Spidermonkey, servos JavaScriptEngine based on Spidermonkey with a small patchset.
+- ci-runners: Various things for servo CI (Continuous Integration).
+- wpt: Servo's fork the the Web Platform Tests
+- _stylo_: Servos CSS engine based on Firefox CSS engine.
+- html5ever: HTML5 high-performance parser.
+- media: media backends and similar that servo uses.
+- book: This book!
+- _webrender_: A fork of Firefox's webrender with a small patchset
+- **Ipc-channel**: Crate for the rust ecosystem of making IPC work.
+- **Surfman**: Low-Level cross platform Rust library for managing graphic surfaces.
+- **unicode-bidi**: Unicode Bidirectional Algorithm implementation.
+- rust-content-security-policy: Content Security Policy crate.
+- **string-cachen**: String interning library.
+- **MallocSizeOf**: Measuring the runtime size of a value to use memory calculation.
+- **Euclid**: Geometric types.
+- **Pathfinder**: GPU-based rasterizer for fonts and vector graphics.