Update scdl-schema.md

Signed-off-by: polinabinder1 <pbinder@nvidia.com>

Author: polinabinder1

sub-packages/bionemo-scdl/docs/scdl-schema.md

@@ -44,7 +44,7 @@ The header is a binary file that contains the metadata for the archive. It is st
   - Name: The name of the array. This is stored as a string.
   - Length: The length of the array. This is stored as a single integer.
   - Dtype: The dtype of the array. This is stored as a string based on an enum.
-  - (Optional) Shape: The shape of the array. This is stored as a list of integers.
+  - [Optional] Shape: The shape of the array. This is stored as a list of integers.
 
 #### Archive Header Spec: