Mention tracing-actix-web in lib-level docs.

Author: LukeMathWalker

tracing/src/lib.rs

@@ -779,6 +779,7 @@
 //!    [OpenTelemetry]-compatible distributed tracing systems.
 //!  - [`tracing-honeycomb`] Provides a layer that reports traces spanning multiple machines to [honeycomb.io]. Backed by [`tracing-distributed`].
 //!  - [`tracing-distributed`] Provides a generic implementation of a layer that reports traces spanning multiple machines to some backend.
+//!  - [`tracing-actix-web`] provides `tracing` integration for the `actix-web` web framework.
 //!  - [`tracing-actix`] provides `tracing` integration for the `actix` actor
 //!    framework.
 //!  - [`tracing-gelf`] implements a subscriber for exporting traces in Greylog