docs(guides): extend Crypt4GH_proTES tutorial with use case example

Author: Valentin Schneider-Lunitz

docs/guides/guide-admin/crypt4gh_to_protes.md

@@ -2,6 +2,23 @@
 
 This guide explains how to configure and deploy an environment that enables encryption and decryption of sensitive data files using TES/[Funnel](https://github.com/ohsu-comp-bio/funnel) with [proTES](https://github.com/elixir-cloud-aai/proTES) as a stable and scalable [GA4GH TES](https://github.com/ga4gh/task-execution-schemas) gateway.
 
+## Use Case
+
+Imagine you are a researcher who needs to analyse sensitive data in a cloud environment. You need to ensure:
+
+- **Your data is encrypted during transfer**: Your files are encrypted for transfer. Raw sensitive data remains located at your storage.
+- **Only authorized researcher can decrypt the data**: Data can only be decrypted with specific private keys. Data theft is useless without specific keys. 
+- **Automatic decryption**: Your setup does automatic decryption given `.c4gh` files and the correct private key.
+- **Secure collaboration**: Data exchange between collaborators is not restricted, as long as the correct key is available.
+
+This tutorial presents a solution where:
+
+1. A data provider encrypts sensitive data using Crypt4GH before uploading them to storage.
+2. Encrypted data is sent to a `Task Execution Service (TES)` instance via `proTES` and a `proTES middleware` for processing.
+3. A researcher (recipient) can process these files in a secure containerized environment where automatic decryption happens using the `proTES middleware`.
+
+This approach allows collaborative research where sensitive data can be processed in cloud environments while maintaining strict access controls and encryption throughout the data lifecycle.
+
 ## Overview
 
 [Crypt4GH](https://crypt4gh.readthedocs.io/) is a standard for encrypting sensitive genomic data. This setup demonstrates:
@@ -13,9 +30,11 @@ This guide explains how to configure and deploy an environment that enables encr
 
 **Security Note:** Private keys should be stored in secure locations and used only for decryption. Consider using signed URLs for transferring private keys to the TES instance. 
 
-## Workflow
+**Goal of this tutorial:** You'll have a setup where you can submit encrypted files via task inputs, and they will be automatically decrypted and processed, ensuring that sensitive data remains protected.
+
+## Setup
 
-The complete workflow consists of three main tasks:
+The complete setup consists of three main tasks:
 
 1. **Key Generation**: Generate Crypt4GH key pairs for the sender and recipient parties (optional).
 2. **File Encryption**: Encrypt sensitive data using the generated keys.