Updating basic example in doc

doc/source/getting-started/quickstart.rst

@@ -48,11 +48,9 @@ Basic example
 """""""""""""
 
 The following is a basic example to execute a two qubit circuit and print the final state in dense vector form using quimb backend::
-
-   # Set the quimb backend
-   qibo.set_backend(
-       backend="qibotn", platform="qutensornet", runcard=computation_settings
-   )
+   
+   import qibo
+   from qibo import Circuit, gates
 
    # Set the runcard
    computation_settings = {
@@ -62,6 +60,13 @@ The following is a basic example to execute a two qubit circuit and print the fi
        "expectation_enabled": False,
    }
 
+
+   # Set the quimb backend
+   qibo.set_backend(
+       backend="qibotn", platform="qutensornet", runcard=computation_settings
+   )
+
+
    # Construct the circuit with two qubits
    c = Circuit(2)