add a note about non-transforming transformers (e.g. caches)

Author: jstriebel

docs/protocol/core/v3.0.rst

@@ -1576,7 +1576,9 @@ Storage transformers
 A Zarr storage transformer allows to change the zarr-compatible data before storing it.
 The stored transformed data is restored to its original state whenever data is requested
 by the Array. Storage transformers can be configured per array via the
-``storage_transformers`` name in the `array metadata`_.
+``storage_transformers`` name in the `array metadata`_. Storage transformers which do
+not change the storage layout (e.g. for caching) may be specified at runtime without
+adding them to the array metadata.
 
 A storage transformer serves the same `Abstract store interface`_ as the store_.
 However, it should not persistently store any information necessary to restore the original data,
@@ -1585,7 +1587,7 @@ From the perspective of an Array or a previous stage transformer both store and
 protocol and can be interchanged regarding the protocol. The behaviour can still be different,
 e.g. requests may be cached or the form of the underlying data can change.
 
-Storage Transformers may be stacked to combine different functionalities:
+Storage transformers may be stacked to combine different functionalities:
 
 .. mermaid::