Update sdk.md

specification/resource/sdk.md

@@ -137,7 +137,7 @@ has higher priority.
 
 The `OTEL_RESOURCE_ATTRIBUTES` environment variable will contain of a list of
 key value pairs, and these are expected to be represented in a format matching
-to the [W3C Baggage](https://w3c.github.io/baggage), except that additional
+to the [W3C Baggage](https://www.w3.org/TR/baggage/#header-content), except that additional
 semi-colon delimited metadata is not supported, i.e.: `key1=value1,key2=value2`.
 All attribute values MUST be considered strings and characters outside the
 `baggage-octet` range MUST be percent-encoded.