chore: update readme

Author: sleepyfoodie

README.md

@@ -56,6 +56,19 @@ Maintainers can trigger the [release workflow](.github/workflows/release.yaml) b
 
 We wanted to backfill `release-0.1` to `release-0.12` to have a changelog, but we were not able to use a GitHub action in a newer commit to trigger a release that generates a changelog on older commits. See #489 for full discussion.
 
+## Metrics Deprecation
+
+The following recording rule is marked deprecated. They will be removed in v2.0.0.
+   ```bash
+   node_namespace_pod_container:container_cpu_usage_seconds_total:sum_irate
+   ```
+It will be replaced by the following recording rule to
+- use `rate` over `irate` in favour of preserving more points of data
+- add `5m` in recording rule name to indicate rate
+   ```bash
+   node_namespace_pod_container:container_cpu_usage_seconds_total:sum_rate5m
+   ```
+
 ## How to use
 
 This mixin is designed to be vendored into the repo with your infrastructure config. To do this, use [jsonnet-bundler](https://github.com/jsonnet-bundler/jsonnet-bundler):