Improve prompb/readme.md (#17037)

* Improve propb/readme.md

Signed-off-by: pipiland2612 <nguyen.t.dang.minh@gmail.com>

* commit

Signed-off-by: pipiland2612 <nguyen.t.dang.minh@gmail.com>

---------

Signed-off-by: pipiland2612 <nguyen.t.dang.minh@gmail.com>

prompb/README.md

@@ -1,9 +1,53 @@
-The compiled protobufs are version controlled and you won't normally need to
-re-compile them when building Prometheus.
+This directory contains Protocol Buffer (protobuf) definitions for Prometheus'
+remote read and write protocols. These definitions are used to serialize and
+deserialize time series data, such as metrics, labels, samples, and queries,
+for network communication to Prometheus.
 
-If however you have modified the defs and do need to re-compile, run
-`make proto` from the parent dir.
+The files here are synced to [buf.build](https://buf.build/prometheus/prometheus),
+a public protobuf schema registry, from the `main` branch of the Prometheus
+repository.
 
-In order for the [script](../scripts/genproto.sh) to run, you'll need `protoc` (version 3.15.8) in
-your PATH.
+## What This Package/Directory Hosts
 
+Protobuf messages and services for:
+- Remote Write: Sending time series data to Prometheus (e.g., `WriteRequest`,
+  `TimeSeries`).
+- Remote Read: Querying data from Prometheus (e.g., `ReadRequest`, `Query`,
+  `ChunkedReadResponse`).
+- Core types: Shared definitions like `Label`, `MetricMetadata`, and exemplars.
+
+Key files include:
+- `remote.proto`: Defines the remote read/write services and messages.
+- `types.proto`: Common types used across protocols.
+- `io/prometheus/client/metrics.proto`: Client metrics definitions.
+- `io/prometheus/write/v2/types.proto`: Remote Write v2 protocol types.
+
+## Stability Guarantees
+
+These protobuf definitions follow the stability policies of the Prometheus
+project. Backward-compatible changes may occur in minor releases, but breaking
+changes are reserved for major versions (e.g., Prometheus 3.0). Experimental
+or unstable features are clearly marked in the documentation.
+
+## Related Specifications
+
+- Remote Write Spec v1:
+  [https://prometheus.io/docs/specs/remote_write_spec/](https://prometheus.io/docs/specs/remote_write_spec/).
+- Remote Write Spec v2:
+  [https://prometheus.io/docs/specs/prw/remote_write_spec_2_0/](https://prometheus.io/docs/specs/prw/remote_write_spec_2_0/).
+- Experimental Prometheus client packages:
+  [https://github.com/prometheus/client_golang/tree/main/exp](https://github.com/prometheus/client_golang/tree/main/exp).
+
+## How to Change or Contribute
+
+To modify these definitions, view and edit the source in the Prometheus GitHub
+repository: [https://github.com/prometheus/prometheus/tree/main/prompb](https://github.com/prometheus/prometheus/tree/main/prompb).
+
+## How to Use
+
+### Steps
+
+- Run `make proto` in the root directory to regenerate the compiled protobuf
+  code.
+- The compiled Go code is version-controlled in the repository, so you
+  typically don't need to re-generate unless making changes.