Added clarifications of directory structure in getting started guide

Signed-off-by: Piet Gömpel <pietgoempel@gmail.com>

Author: Pietfried

doc/common/getting_started.md

@@ -42,6 +42,15 @@ make -j$(nproc) install
 
 Run any required tests from build/tests.
 
+## Clarifications for directory structures, namespaces and OCPP versions
+
+This repository contains multiple subdirectories and namespaces named v16, v2 and v21.
+
+* The v16 directories contain files for configuring and implementing OCPP 1.6.
+* The v2 directories include files for both OCPP2.0.1 and OCPP2.1, as OCPP 2.1
+is fully backward compatible with OCPP 2.0.1.
+* The v21 directories include files only for OCPP2.1.
+
 ## Get Started with OCPP1.6
 
 Please see the [Getting Started documentation for OCPP1.6](../v16/getting_started.md).