Update Sources/Instrumentation/Instrument.swift

Co-authored-by: Konrad `ktoso` Malawski <[email protected]>

Author: heckj

Sources/Instrumentation/Instrument.swift

@@ -18,6 +18,9 @@ import ServiceContextModule
 ///
 /// The assocaited type, `Carrier`, is a service request such as an HTTP request,
 /// that has string values that can be extracted to provide information for a tracing span.
+///
+/// Typically the library adopting instrumentation, would provide an implementation of this type, since it is aware of its carrier type. 
+/// Which then can be combined with instrumentation or tracing implementations, which are not aware of the concrete carrier, and only provide an ``Instrument`` (or `Tracer`) which makes use of injector/extractor to operate on carrier values.
 public protocol Extractor: Sendable {
     /// The carrier to extract values from.
     associatedtype Carrier: Sendable