Document codespaces.disableAutomaticConfiguration (#1132)

* Document `codespaces.disableAutomaticConfiguration`

* Update src/universal/README.md

Co-authored-by: Samruddhi Khandale <samruddhikhandale@github.com>

* Update src/universal/README.md

Co-authored-by: Samruddhi Khandale <samruddhikhandale@github.com>

---------

Co-authored-by: Samruddhi Khandale <samruddhikhandale@github.com>

Author: cmbrose

src/universal/README.md

@@ -53,6 +53,19 @@ Alternatively, you can use the contents of [.devcontainer](.devcontainer) to ful
 
 Refer to [this guide](https://containers.dev/guide/dockerfile) for more details.
 
+## Disabling Automatic Setup in Codespaces
+
+Codespaces will automatically perform some default setup when the `universal` image is used and no `postCreateCommand` is provided. This can be disabled with the `customizations.codespaces.disableAutomaticConfiguration` setting:
+
+```jsonc
+"customizations": {
+	// Configure properties specific to Codespaces.
+	"codespaces": {
+		"disableAutomaticConfiguration": true
+	}
+}
+```
+
 ## License
 
 Copyright (c) Microsoft Corporation. All rights reserved.