add config tutorial

Author: commit111

docs/tutorials/configure-environment-variables.md

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+---
+sidebar_position: 400
+title: Configure Environment Variables
+description: How to configure sensitive environment variables in Defang.
+---
+
+# Configure Environment Variables
+
+
+This tutorial will show you how to configure sensitive environment variables in Defang.
+
+## Pre-requisites
+* [A `compose.yaml` file in your project](https://docs.docker.com/compose/gettingstarted/)
+* [A Defang Account](/docs/concepts/authentication)
+* [The Defang CLI](/docs/getting-started#install-the-defang-cli)
+
+## Step 1 - Go to your `compose.yaml` file
+:::info 
+If you are using [Pulumi](/docs/concepts/pulumi) instead of Compose files to define your application, please see [Using Config With Pulumi](/docs/concepts/configuration#using-config-with-pulumi).
+:::
+
+In your Compose file, you can define a sensitive config variable for your service by leaving it as a **blank or `null` value**. Defang will recognize it as a sensitive value. 
+
+In the example below, let's define `API_KEY` as an environment variable.
+
+```yaml
+services:
+  service1:
+    image: image1:latest
+    environment:
+      - API_KEY
+```
+
+The type of notation shown above is called *list notation*. Alternatively, you can use *map notation*, which is also acceptable:
+```yaml
+services:
+  service1:
+    image: image1:latest
+    environment:
+      API_KEY:
+```
+
+## Step 2 - Set the actual value in the Defang CLI
+To store the actual (sensitive) value of the variable, open up a terminal and type the command:
+```bash
+defang config set API_KEY=actualvalue
+```
+Remember to replace `API_KEY` with your variable name and `actualvalue` with your actual value. 
+
+:::tip
+You can view all of your config variables by doing `defang config ls`.
+:::
+
+### Editing a config value
+To edit a value, you can run the command again with an updated value to overwrite the current value:
+```bash
+defang config set API_KEY=newvalue
+```
+
+### Removing a config value
+To remove a value, run the command:
+```bash
+defang config rm API_KEY
+```
+:::tip
+Remember to update your Compose file if you remove an environment variable.
+:::
+
+## Step 3 - Deploy
+```bash
+defang compose up
+```
+
+---
+For a deeper discussion on how configuration works in Defang, see our [Configuration docs](/docs/concepts/configuration).