[doc] Add specification related to #30 issue

Author: Grolleau-Benjamin

README.md

@@ -1,4 +1,4 @@
-
+# STSELib
 
 ![STSELib](doc/resources/Pictures/STSELib.png)
 
@@ -11,10 +11,35 @@ The STSELib middleware is composed of three software modules as illustrated in t
 ![STSELib](doc/resources/Pictures/STSELib_arch.png)
 
 <b>- Application Programming Interface (API) layer</b>
-This software layer is the entry point for the system application. It provides a set of high level functions  allowing interaction with STMicroelectronics Secure Elements.
+This software layer is the entry point for the system application. It provides a set of high level functions allowing interaction with STMicroelectronics Secure Elements.
 
 <b>- Service layer</b>
 Provides a set of product services that format all commands supported by the targeted secure element and reports response to higher layers API/Application . This layer can be used directly from Application (for advanced user).
 
 <b>- Core layer</b>
 Contains generic definition for ST Secure Element and functions for communicating with target secure element.
+
+## Integration
+
+### 1. Add STSELib as a Git submodule
+
+From your project root:
+
+```bash
+git submodule add https://github.com/STMicroelectronics/STSELib.git lib/stselib
+git submodule update --init --recursive
+```
+
+> [!NOTE]
+>
+> Don’t forget to add lib/stselib to your CMakeLists.txt include paths.
+
+### 2. Base configuration
+
+Two headers files are mantatories, [`stse_conf.h`](doc/resources/Markdown/03_LIBRARY_CONFIGURATION/03_LIBRARY_CONFIGURATION.md) and [`stse_platform_generic.h`](doc/resources/Markdown/04_PORTING_GUIDE/PAL_files/stse_platform_generic.h.md).
+
+### 3. Optional files
+
+For platform-specific integrations and STSafe use-cases, you may implement additional headers. Detailed specifications are available in the HTML documentation included in the release ZIP.
+
+Sample is available on Grom-'s github : [STSAFE-A_Accessory_authentication](https://github.com/Grom-/STSAFE-A_Accessory_authentication). The platform files are located in the `Platforms/NUCLEO-L452RE/STSELib` directory.