Add comantary about async api of the session storage.
Add comantary about async api of the session storage.

funcool/catacumba,mitchelkuijpers/catacumba,funcool/catacumba,coopsource/catacumba,prepor/catacumba,prepor/catacumba,mitchelkuijpers/catacumba,funcool/catacumba,coopsource/catacumba