Store configuration documentation missing

[DanielBadura]

We already had a PR fixing the docs (#216) about the table_name, that this is located under options. This extra layer was introduced since we now have more options at hand. For example to configure the locking of the store (patchlevel/event-sourcing#613) and soon from the stream store (patchlevel/event-sourcing#620). We should add the config param into the docs.