Add update command (#53)

Before this commit, updating Pixel required a `git pull` followed by a
`./pixel.js clean` which can be tedious. Instead, promote the updating
process as a CLI command:

```sh
./pixel.js update
```

README.md

@@ -101,21 +101,17 @@ If you want to stop all of Pixel's services, run:
 
 ### Updates
 
-Updating Pixel is more of a hassle than it should be. It requires two steps:
+Updating Pixel to the latest version is more of a hassle than it should be. It
+requires:
 
 ```sh
-git pull
+./pixel.js update
 ```
 
-which pulls down the latest code. Then run:
-
-```sh
-./pixel.js clean
-```
-
-The `clean` command destroys all Docker images, containers, and volumes
-associated with Pixel and ensures that the necessary Docker images are rebuilt with the latest.
-If the Docker images are updated and you don't run this command, you will likely get errors.
+This command will pull the latest code and destroy all Docker images,
+containers, and volumes associated with Pixel to ensure that it is using the
+latest database seed data and that the necessary Docker images are rebuilt with
+the latest code. As a result, updates can take awhile.
 
 ### Cleanup
 

pixel.js

@@ -251,6 +251,17 @@ function setupCli() {
 			);
 		} );
 
+	program
+		.command( 'update' )
+		.description( 'Updates Pixel to the latest version. This command also destroys all containers, images, networks, and volumes associated with Pixel to ensure it is using the latest code.' )
+		.action( async () => {
+			await batchSpawn.spawn(
+				'git',
+				[ '-C', __dirname, 'fetch', 'origin', 'main:main' ]
+			);
+			await cleanCommand();
+		} );
+
 	program
 		.command( 'clean' )
 		.description( 'Removes all containers, images, networks, and volumes associated with Pixel so that it can start with a clean slate. If Pixel is throwing errors, try running this command.' )