Clarify the reason of using LSMOnly options as a default

[burdiyan]

I wonder why this package uses Badger's LSMOnlyOptions as a default https://github.com/ipfs/go-ds-badger/blob/master/datastore.go#L85

As it is quite a fine tuning setting for Badger would be nice to have documented the reason for using it.

[welcome]

Thank you for submitting your first issue to this repository! A maintainer will be here shortly to triage and review.
In the meantime, please double-check that you have provided all the necessary information to make this process easy! Any information that can help save additional round trips is useful! We currently aim to give initial feedback within two business days. If this does not happen, feel free to leave a comment.
Please keep an eye on how this issue will be labeled, as labels give an overview of priorities, assignments and additional actions requested by the maintainers:

• "Priority" labels will show how urgent this is for the team.
• "Status" labels will show if this is ready to be worked on, blocked, or in progress.
• "Need" labels will indicate if additional input or analysis is required.

Finally, remember to use https://discuss.ipfs.io if you just need general support.