Doc: update snippets fot STAC examples

scenes/stac.py

@@ -4,6 +4,9 @@ This module enables various operations from STAC catalogs.
 # Spot-6/7 DRS from Dinamis (experimental)
 
 ```python
+import dinamis_sdk
+from stac_client import Client
+
 api = Client.open(
     'https://stacapi-dinamis.apps.okd.crocc.meso.umontpellier.fr',
     modifier=dinamis_sdk.sign_inplace,
@@ -23,6 +26,9 @@ for item in res.items():
 # Sentinel-2 images from Microsoft planetary computer
 
 ```python
+import planetary_computer
+from stac_client import Client
+
 api = Client.open(
     'https://planetarycomputer.microsoft.com/api/stac/v1',
     modifier=planetary_computer.sign_inplace,