docs: Update docs about busola-kyma image (#3402)

* update docs about busola-kyma image

* fix-fmt

* Apply suggestions from code review

Co-authored-by: Grzegorz Karaluch <[email protected]>

* fix fmt

---------

Co-authored-by: Grzegorz Karaluch <[email protected]>

README.md

@@ -155,7 +155,9 @@ When developing new features in Busola, adhere to the following rules. This will
 
 For the information on how to run tests and configure them, go to the [`tests`](tests) directory.
 
-## Busola in Docker: adding a cluster via kubeconfig ID
+## Busola in Docker
+
+### Adding a cluster using kubeconfig ID
 
 1. If you run Busola in Docker, you can mount your kubeconfig as a bind mount for Busola container. Execute the following command:
 
@@ -165,6 +167,17 @@ For the information on how to run tests and configure them, go to the [`tests`](
 
 2. When you open Busola in your browser, go to `http://localhost:3001?kubeconfigID={YOUR_KUBECONFIG_FILE_NAME}`. Busola will try to download that file and add it for your Busola instance.
 
+### Set active environment
+
+1. To use one of the built-in environments in the `busola-kyma` image (dev, stage, prod), pass env `ENVIRONMENT` to the Docker container.
+   ```bash
+   docker run --rm -it -p 3001:3001 -v --env ENVIRONMENT={your-env}--pid=host --name busola europe-docker.pkg.dev/kyma-project/prod/busola-kyma-web:latest
+   ```
+2. To use a custom environment configuration, mount it in Docker and pass the `ENVIRONMENT` env to the Docker container.
+   ```bash
+   docker run --rm -it -p 3001:3001 -v <path to your custom config>:/app/core-ui/environments/ --env ENVIRONMENT={your-env} --pid=host --name busola europe-docker.pkg.dev/kyma-project/prod/busola:latest
+   ```
+
 ## Troubleshooting
 
 > **TIP:** To solve most of the problems with Busola development, clear the browser cache or do a hard refresh of the website.