appending note in docs

docs/composition/styles.md

@@ -32,6 +32,21 @@ If using the {class}`pangeo_forge_recipes.transforms.ConsolidateDimensionCoordin
 
 ```
 
+```{note}
+{class}`pangeo_forge_recipes.transforms.StoreToZarr` supports appending to existing Zarr stores
+via the optional `append_dim` keyword argument. This option functions nearly identically to the
+`append_dim` kwarg in
+[`xarray.Dataset.to_zarr`](https://docs.xarray.dev/en/latest/generated/xarray.Dataset.to_zarr.html);
+the two differences with this method are that Pangeo Forge will automatically introspect the inputs in
+your {class}`FilePattern <pangeo_forge_recipes.patterns.FilePattern>` to determine how the existing Zarr
+store dimensions need to be resized, and that writes are parallelized via Apache Beam. Apart from
+ensuring that the named `append_dim` already exists in the dataset to which you are appending, use of
+this option does not ensure logical consistency (e.g. contiguousness, etc.) of the appended data. When
+selecting this option, it is therefore up to you, the user, to ensure that the inputs provided in the
+{doc} `file pattern <file_patterns>` for the appending recipe are limited to those which you want to
+append.
+```
+
 
 ## Open with Kerchunk, write to virtual Zarr