started outlining possible compose page outline

Author: linda

docs/concepts/compose-support.md

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+---
+title: Compose Support
+description: Defang supports many of the properties of the Compose specification.
+sidebar_position: 160
+---
+
+# Compose Support
+
+This page outlines what properties of the [Compose specification](https://docs.docker.com/compose/compose-file/) Defang supports when writing a `compose.yaml` file.
+For a more general overview of how Defang works with Compose, please see our [Compose](/docs/concepts/compose) page.
+
+### Supported Compose Properties
+|Property | Details
+|-|-
+|`image` | 
+
+### Optional Compose Properties
+|Property | Details
+|-|-
+|`ports` | If left unspecified, a random port will be chosen. 
+|`memory` | If left unspecified, will resort to default. 
+|`environment` | 
+
+### Depreciated Compose Properties
+|Property | Details
+|-|-
+|`version` | This top-level element is no longer needed in the Compose file. Instead, Defang uses the most recent schema supported for parsing the file.
+
+### Unsupported Compose Properties
+|Property | Details
+|-|-
+|`volume` | Volume mounts are not currently supported by Defang, but will not break the file if included. 
+
+
+
+### Configuration
+You can define sensitive environment variables/configuration for Defang by writing out the variable name and leaving it in as a blank or `null` value in the Compose file. See our [Configuration](/docs/concepts/configuration) page for more.