test: document the Azure setup process

The image tests are now able to upload images to Azure and boot them there.
However, the documentation on how to set up the required resources in Azure
was missing. This commit adds it.

test/README.md

@@ -30,6 +30,65 @@ boot-test the image.
 To (re)generate these test cases use the tool
 `tools/test-case-generators/generate-test-cases`.
 
+### Setting up Azure upload tests
+
+By default, the vhd images are run locally using qemu. However, when
+the right set of environment flags is passed to the osbuild-image-tests,
+it uploads the image to Azure, boots it and tries to ssh into it.
+
+#### Required flags
+- `AZURE_STORAGE_ACCOUNT`
+- `AZURE_STORAGE_ACCESS_KEY`
+- `AZURE_CONTAINER_NAME`
+- `AZURE_SUBSCRIPTION_ID`
+- `AZURE_CLIENT_ID`
+- `AZURE_CLIENT_SECRET`
+- `AZURE_TENANT_ID`
+- `AZURE_LOCATION`
+- `AZURE_RESOURCE_GROUP`
+
+#### Setting up all the required resources
+
+1) Firstly, go to *Subscriptions* in the left-side menu. Here you can find
+   the `AZURE_SUBSCRIPTION_ID`.
+
+2) Now, you need to create a new resource group. In the left-side menu,
+   select *Resource groups*. Click on *Add* above the resource group list.
+   The name you choose is your `AZURE_RESOURCE_GROUP`. The region you choose
+   is your `AZURE_LOCATION`. However, it must be in the "machine-readable
+   form". You can list all the locations with their machine-readable names
+   using Azure CLI: `az account list-locations -o table`.
+   E.g. the machine-readable name of US East location is `eastus`.
+   
+   Note that terms *location* and *region* are synonyms in Azure's context.
+
+3) Storage time! Go to Storage accounts in the left-side menu. Click on
+   *Add* above the list. Use the resource group you created in
+   the previous step. Also, the region should be the same. The name you
+   choose is your `AZURE_STORAGE_ACCOUNT`.
+
+   After the storage account is created, open it.
+   Select *Settings > Access keys*. Choose one of the keys, this is your
+   `AZURE_STORAGE_ACCESS_KEY`. Select *Blob service > Containers* and create
+   a new one. Its name is your `AZURE_CONTAINER_NAME`.
+
+4) Now it’s time to create an application. This is needed because Azure uses
+   OAuth to do authorization. In the left-side menu, choose *Azure Active
+   Directory*. Go to *Manage > App registrations* and register a new
+   application.
+
+   When it’s created, open it. In the overview, you can see
+   the Application (client) ID and the Directory (tenant) ID. These are your
+   `AZURE_CLIENT_ID` and `AZURE_TENANT_ID`.
+
+   Now, go to *Manage > Certificates & Secrets* under your new application
+   and create a new client secret. The is your `AZURE_CLIENT_SECRET`.
+
+5) The last step is to give the new application access to the resource group.
+   This step must be done by Azure administrator (@larskarlitski): Go to
+   the *Access control (IAM)* section under the newly created resource group.
+   Here, add the new application with the *Developer* role.
+
 ## Notes on asserts and comparing expected values
 
 When comparing for expected values in test functions you should use the