add guide for manual user onboarding

docs/tech/security.md

@@ -40,6 +40,8 @@ but it is not necessary because ADMIN has control over every resource on the pla
 
 ## User onboarding
 
+### Authomatically
+
 Users can be added to the platform via a `.csv` file in the following format:
 
 ```
@@ -74,3 +76,23 @@ Admin can be created only by admin users.
 As a separator for the column, you can use either `,` or `;`.
 
 An example of such a file can be [downloaded](https://gitlab.fi.muni.cz/inject/inject-docs/-/raw/main/docs/tech/example_csv.csv?ref_type=heads&inline=false).
+
+### Manually
+
+Another way of adding users is manually via the console:
+
+ - List the running Docker containers to find the **NAME** of the backend container:
+    ```
+    docker ps
+    ```
+ - Execute a shell session in the backend container. Replace `CONTAINERNAME` with the actual container **NAME** of the backend service:
+    ```
+    docker exec -it CONTAINERNAME python manage.py shell
+    ```
+
+- Create a user using the Django shell. Replace `email@test.com` and `password` with your desired user credentials.:
+
+    ``` python
+    from user.models import User
+    User.objects.create_user(username="email@test.com", password="password")
+    ```
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