docs(changelog): new metrics

docs/changelogs/v0.31.md

@@ -6,13 +6,20 @@
 
 - [Overview](#overview)
 - [🔦 Highlights](#-highlights)
+  - [New metrics](#new-metrics)
 - [📝 Changelog](#-changelog)
 - [👨‍👩‍👧‍👦 Contributors](#-contributors)
 
 ### Overview
 
 ### 🔦 Highlights
 
+#### New metrics
+
+- Added 3 new go metrics: `go_gc_gogc_percent`, `go_gc_gomemlimit_bytes` and `go_sched_gomaxprocs_threads` as those are [recommended by the Go team](https://github.com/prometheus/client_golang/pull/1559)
+- Added [network usage metrics](https://github.com/prometheus/client_golang/pull/1555): `process_network_receive_bytes_total` and `process_network_transmit_bytes_total`
+- Removed `go_memstat_lookups_total` metric [which was always 0](https://github.com/prometheus/client_golang/pull/1577)
+
 ### 📝 Changelog
 
 ### 👨‍👩‍👧‍👦 Contributors