docs(getting-started): add section on using environment variables

Add a new section to the "Getting started" guide, explaining how to access environment variables in the application using the `useAppEnvironmentVariables` hook from `@equinor/fusion-framework-react-app`.

Add  a code example demonstrating the usage of the hook.

.changeset/add-doc-environment-variables.md

@@ -0,0 +1,7 @@
+---
+'@equinor/fusion-framework-docs': patch
+---
+
+## @equinor/fusion-framework-docs
+
+Updated the "Getting started" guide with a new section about using environment variables.

vue-press/src/guide/app/getting-started.md

@@ -122,6 +122,31 @@ export default () => ({
 
 :::
 
+#### Environment variables
+
+To access the environment variables in the application, use the hook `useAppEnvironmentVariables` from `@equinor/fusion-framework-react-app`.
+
+```ts
+import { useAppEnvironmentVariables } from '@equinor/fusion-framework-react-app';
+
+type AppEnvironmentVariables = {
+  API_URL: string;
+  API_SCOPE: string;
+}
+
+const MyComponent = () => {
+  const env = useAppEnvironmentVariables<AppEnvironmentVariables>();
+  console.log(env); // { API_URL: 'https://foo.bar', API_SCOPE: 'c5161f15-9930-4cfc-b233-e9dfc5f8ad82/.default' }
+}
+```
+
+> [!INFO]
+> The `useAppEnvironmentVariables` hook consumes asyncronous data from the app service.
+> In theory the value should always be available, since loaded during configuration.
+>
+> There will be a future module which manages application state, where during the configuration the 
+> desired environment variables can be picked.
+
 ## Creating Application
 
 ### Main