README: Initial introduction.

README.md

@@ -1,2 +1,18 @@
-# ldraw
-ldraw library and tools with version control
+# LDraw
+
+This is a mirror of the LDraw LEGO parts library available at [ldraw.org](https://www.ldraw.org/). It is the same collection of parts, but with all the benefits of version control. See also the original LDraw [Readme.txt](Readme.txt).
+
+### Usage
+
+```
+git clone https://github.com/pybricks/ldraw.git
+```
+
+This creates the `ldraw` folder. Use it like you always do.
+
+
+### Changes compared to the official `complete.zip` parts pack:
+- Full Git history since the 2008 re-release.
+- Fixed [`mklist`](./mklist) source code. The `exe` files are unchanged.
+- Includes [`lsynth`](./lsynth) source code and dependencies.
+