Document gltf and glb tsci export formats

docs/command-line/tsci-export.md

@@ -40,6 +40,8 @@ The following export formats are supported:
 | `pcb-svg` | PCB layout as SVG |
 | `readable-netlist` | Human-readable netlist |
 | `specctra-dsn` | Specctra DSN format for autorouting |
+| `gltf` | Text-based 3D scene (glTF 2.0) that references board meshes and textures |
+| `glb` | Binary glTF bundle that packs geometry, materials, and textures into a single file |
 
 ## Examples
 
@@ -63,6 +65,28 @@ Export to Specctra DSN format:
 tsci export circuit.tsx -f specctra-dsn
 ```
 
+## Exporting 3D models
+
+Use the `gltf` or `glb` formats when you want a 3D representation of your board for use in CAD tools, AR viewers, or when embedding on the web.
+
+### Export as glTF
+
+```bash
+tsci export circuit.tsx --format gltf
+```
+
+This produces a `.gltf` file (plus any referenced texture files) that follows the [glTF 2.0](https://www.khronos.org/gltf/) spec. Because the assets stay separate, glTF exports are easier to diff in git and you can selectively optimize textures.
+
+### Export as GLB
+
+```bash
+tsci export circuit.tsx --format glb
+```
+
+The `glb` format wraps the same data into a single binary so you can upload one file to a web viewer (for example, https://gltf.report/ or `model-viewer`). This is handy for sharing previews or attaching a lightweight CAD model to a manufacturing request.
+
+Both commands work with `.tsx` source files as well as `.circuit.json` files, so you can export whichever representation you already have. Each command writes the 3D model next to the input file unless you override the location with `--output <path>`.
+
 ## Output Files
 
 By default, the exported file will be saved in the same directory as the input file, with a filename based on the input filename and the chosen format. For example: