NIP-03: explain why a single attestation is recommended.

Author: fiatjaf

03.md

@@ -20,7 +20,7 @@ This NIP defines an event with `kind:1040` that can contain an [OpenTimestamps](
 ```
 
 - The OpenTimestamps proof MUST prove the referenced `e` event id as its digest.
-- The `content` MUST be the full content of an `.ots` file containing at least one Bitcoin attestation. This file SHOULD contain a **single** Bitcoin attestation and no reference to "pending" attestations since they are useless in this context.
+- The `content` MUST be the full content of an `.ots` file containing at least one Bitcoin attestation. This file SHOULD contain a **single** Bitcoin attestation (as not more than one valid attestation is necessary and less bytes is better than more) and no reference to "pending" attestations since they are useless in this context.
 
 ### Example OpenTimestamps proof verification flow