Document how BatteryPool instances should be created

Signed-off-by: Sahas Subramanian <[email protected]>

Author: shsms

src/frequenz/sdk/timeseries/battery_pool/_battery_pool.py

@@ -39,8 +39,10 @@
 class BatteryPool:
     """An interface for interaction with pools of batteries.
 
-    Use the [microgrid.battery_pool][frequenz.sdk.microgrid.battery_pool] method for
-    creating `BatteryPool` instances.
+    !!! note
+        `BatteryPool` instances are not meant to be created directly by users.  Use the
+        [`microgrid.battery_pool`][frequenz.sdk.microgrid.battery_pool] method for
+        creating `BatteryPool` instances.
 
     Provides:
       - properties for fetching reporting streams of instantaneous
@@ -63,6 +65,11 @@ def __init__(
     ):
         """Create a BatteryPool instance.
 
+        !!! note
+            `BatteryPool` instances are not meant to be created directly by users.  Use
+            the [`microgrid.battery_pool`][frequenz.sdk.microgrid.battery_pool] method
+            for creating `BatteryPool` instances.
+
         Args:
             battery_pool_ref: The battery pool reference store instance.
             name: An optional name used to identify this instance of the pool or a