add Note

Author: huppd

README.md

@@ -177,6 +177,14 @@ This will:
 - Export `requirements.txt` (production)
 - Export `requirements_dev.txt` (dev/test)
 
+> **Note:**  
+> In Poetry 2.0 and later, the `export` command is provided by the optional  
+> plugin `poetry-plugin-export`. If you see  
+> `The requested command export does not exist`, install the plugin with:
+> ```console
+> poetry self add poetry-plugin-export
+> ```
+
 ### Release a new probtest version
 
 Release versions use two digits only: the first digit represents breaking major