[database] Add information about the new optional environment field

Requires beat/beat/core> to be at least 1.10.5

doc/databases.rst

@@ -130,15 +130,25 @@ Each database has a JSON_ declaration. This file has the information about the p
 	            "template": "simple_face_recognition"
 	        }
 	    ],
-	    "root_folder": "/path_to_db_folder/att_faces"
+	    "root_folder": "/path_to_db_folder/att_faces",
+        "environment": {
+            "name": "Databases",
+            "version": "1.0.0"
+        }
 	}
 
-The JSON_ file for a database has three main field.
+The JSON_ file for a database has three main field:
 
 * **description:** A short description of the database.
 * **protocols:** a list of protocols defined for the database.
 * **root_folder:** path to the directory where the data is stored.
 
+and one optional field:
+
+* **environment:** The name and version of the runtime environment to use for this database.
+
+If the environment field is not given, the system will try to find an appropriate environment using the database name as reference. If no database environment declares support for the database, then the execution will fail.
+
 The "protocols" field is where the datasets for each protocol is defined. In the example above only one protocol is defined. Implementing a new protocol means adding a new entry to the list of protocols. Each protocol has three main component:
 
 * **name:** The name of the protocol which is "idiap" in this case.