Document the usage of with_transaction with example

[rodolfoBee]

SDK

Rust SDK

Description

The usage of it is not documented in the official docs: https://docs.sentry.io/platforms/rust/

https://docs.rs/sentry-actix/0.38.1/sentry_actix/struct.Sentry.html

Suggested Solution

Add to the documentation with usage examples for Sentry users.