Add command options and documentation to Docker Compose

This commit introduces the command configuration for the bandersnatch service in Docker Compose setup.
It includes the default 'mirror' command and adds commented options for 'verify' and 'once' to provide alternatives for running bandersnatch.

The 'command' section is now clearly documented, making it easier for developers and sysadmins to understand and modify the behavior of the bandersnatch service.

Changes:
- Added 'command' directive to bandersnatch service with the default 'mirror' option.
- Included comments explaining how to use the 'verify' and 'once' commands.
- Explained the purpose of additional flags for the 'mirror' command.
- Provided documentation for the build context of the bandersnatch_nginx image.

src/bandersnatch_docker_compose/docker-compose.yml

@@ -1,18 +1,31 @@
 services:
+  # The bandersnatch service configuration
   bandersnatch:
-    image: pypa/bandersnatch:latest
+    image: pypa/bandersnatch:latest  # Use the latest version of bandersnatch
     volumes:
-      - "./config:/conf"
-      - "./data:/srv/pypi/web"
+      - "./config:/conf"  # Mount the local configuration directory to the container
+      - "./data:/srv/pypi/web"  # Mount the local data directory where the mirror will be stored
+    command: bandersnatch mirror
+    # Uncomment the command you want to use:
+    # command: bandersnatch verify  # Verifies the integrity of the mirror
+    # command: bandersnatch once    # Runs the mirror operation once and then exits
+
+      # Default command is 'mirror', which synchronizes the mirror with PyPI
+      # You can append additional flags to customize the 'mirror' behavior:
+      # "--force-check" to force a recheck of all packages
+      # "--delete-packages" to remove packages that have been deleted from PyPI
     networks:
-      - bandersnatch_net
+      - bandersnatch_net  # Connects the service to the custom bridge network
+
+  # The nginx service configuration for serving the mirror
   bandersnatch_nginx:
     image: bandersnatch_nginx
+    # If the image not built yet, it will be built from the nginx image from the Dockerfile in the current directory
     build: .
     volumes:
-      - "./data:/data/pypi/web:ro"
+      - "./data:/data/pypi/web:ro"  # Mount the data directory as read-only for nginx
     ports:
-      - "40080:80"
+      - "40080:80"  # Map port 40080 on the host to port 80 in the container
     networks:
       - bandersnatch_net