Refactor Docker setup and update API description

- Updated docker-compose.yml to use context and dockerfile for the app service, and removed unnecessary db service configuration.
- Modified Dockerfile to use the official Rust nightly image and streamlined the build process with updated working directories and runtime dependencies.
- Changed API description in root handler to reflect the correct endpoint for fetching the current hospital.

docker-compose.yml

@@ -2,30 +2,13 @@ version: '3.8'
 
 services:
   app:
-    build: .
+    build:
+      context: .
+      dockerfile: Dockerfile
     ports:
       - "3000:3000"
-    depends_on:
-      - db
     environment:
-      - DATABASE_URL=postgres://postgres:postgres@db/hospitaldb
-      - HOST=0.0.0.0
-      - PORT=3000
-    volumes:
-      - ./.env:/usr/src/app/.env
-    restart: unless-stopped
-
-  db:
-    image: postgres:14
-    environment:
-      - POSTGRES_USER=postgres
-      - POSTGRES_PASSWORD=postgres
-      - POSTGRES_DB=hospitaldb
-    volumes:
-      - postgres_data:/var/lib/postgresql/data
-    ports:
-      - "5432:5432"
-    restart: unless-stopped
-
-volumes:
-  postgres_data: 
+      - HOST=${HOST}
+      - PORT=${PORT}
+      - DATABASE_URL=${DATABASE_URL}
+    restart: unless-stopped