Improve array and group docstringspc

Author: dstansby

src/zarr/core/array.py

@@ -1707,7 +1707,9 @@ def _info(
 # TODO: Array can be a frozen data class again once property setters (e.g. shape) are removed
 @dataclass(frozen=False)
 class Array:
-    """Instantiate an array from an initialized store."""
+    """
+    A Zarr array.
+    """
 
     _async_array: AsyncArray[ArrayV3Metadata] | AsyncArray[ArrayV2Metadata]
 

src/zarr/core/group.py

@@ -1744,6 +1744,10 @@ async def move(self, source: str, dest: str) -> None:
 
 @dataclass(frozen=True)
 class Group(SyncMixin):
+    """
+    A Zarr group.
+    """
+
     _async_group: AsyncGroup
 
     @classmethod