fix(metrics): fix Cargo.toml description and README installation note

- Update description field to accurately reflect Prometheus metrics purpose.
- Add note that crate is not yet published on crates.io and show path dependency.

Author: josecelano

packages/metrics/Cargo.toml

@@ -1,5 +1,5 @@
 [package]
-description = "A library with the primitive types shared by the Torrust tracker packages."
+description = "Prometheus metrics integration library providing type-safe metric collection and aggregation."
 keywords = [ "api", "library", "metrics" ]
 name = "torrust-metrics"
 readme = "README.md"

packages/metrics/README.md

@@ -20,9 +20,11 @@ This library offers a robust metrics system for tracking and monitoring applicat
 
 Add this to your `Cargo.toml`:
 
+> **Note**: This crate is not yet published on crates.io. Use a path or git dependency.
+
 ```toml
 [dependencies]
-torrust-metrics = "3.0.0"
+torrust-metrics = { path = "packages/metrics" }
 ```
 
 ### Basic Usage