[demo] add GPU to resources (facebookresearch#355)

This small PR adds GPU specification in `docker-compose.yaml` for the SAM 2 interactive webdemo, following https://docs.docker.com/compose/how-tos/gpu-support/#example-of-a-compose-file-for-running-a-service-with-access-to-1-gpu-device. It fixes a GPU access error as reported in facebookresearch#354.

(close facebookresearch#354)

docker-compose.yaml

@@ -33,3 +33,10 @@ services:
       - VIDEO_ENCODE_MAX_WIDTH=1280
       - VIDEO_ENCODE_MAX_HEIGHT=720
       - VIDEO_ENCODE_VERBOSE=False
+    deploy:
+      resources:
+        reservations:
+          devices:
+            - driver: nvidia
+              count: 1
+              capabilities: [gpu]