nips : More precisely document since/until bounds. (#1284)

* More precisely document since/until bounds.

Lower in this document, this is expressed as "since <= created_at <= until".

But the English description said that these values had to be "newer than" or "older than".

These two were in conflict. I assume the inclusive behavior is the intended one, since that documentation was added later to clarify. This just makes both cases match.

* Update 01.md

Co-authored-by: Alex Gleason

* Update 01.md

Co-authored-by: Alex Gleason

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Co-authored-by: Alex Gleason

https://github.com/nostr-protocol/nips/commit/8c47577ecb6b3ae6ad840e5b4d187a3f3a6b97c8