Added non-interactive example (#11)

Author: giswqs

docs/usage.md

@@ -2,6 +2,39 @@
 
 To use segment-geospatial in a project:
 
-```
+```python
 import samgeo
 ```
+
+Here is a simple example of using segment-geospatial to generate a segmentation mask from a satellite image:
+
+```python
+import os
+import torch
+from samgeo import SamGeo, tms_to_geotiff
+
+bbox = [-95.3704, 29.6762, -95.368, 29.6775]
+image = 'satellite.tif'
+tms_to_geotiff(output=image, bbox=bbox, zoom=20, source='Satellite')
+
+out_dir = os.path.join(os.path.expanduser('~'), 'Downloads')
+checkpoint = os.path.join(out_dir, 'sam_vit_h_4b8939.pth')
+
+device = 'cuda' if torch.cuda.is_available() else 'cpu'
+sam = SamGeo(
+    checkpoint=checkpoint,
+    model_type='vit_h',
+    device=device,
+    erosion_kernel=(3, 3),
+    mask_multiplier=255,
+    sam_kwargs=None,
+)
+
+mask = 'segment.tiff'
+sam.generate(image, mask)
+
+vector = 'segment.gpkg'
+sam.tiff_to_gpkg(mask, vector, simplify_tolerance=None)
+```
+
+![](https://i.imgur.com/Ysq3u7E.png)