docs: Add additional warning about attributes and span_creation (#1291)
docs: Add additional warning about attributes and span_creation (#1291)

Fixes #1258 by noting that samplers only consider attributes present at span creation.

Co-authored-by: Francis Bogsanyi <670cd5605830f6b63d443687caab7fc24c3610f8@shopify.com>
open-telemetry/opentelemetry-ruby,open-telemetry/opentelemetry-ruby