Special guidance for ECS contribtions during ECS donation (elastic#2325)

CHANGELOG.next.md

@@ -34,6 +34,8 @@ Thanks, you're awesome :-) -->
 
 #### Added
 
+* Documentation in README.md providing instruction on contributions to ECS during the OTel donation #2325
+
 #### Improvements
 
 #### Deprecated

CONTRIBUTING.md

@@ -7,7 +7,8 @@ ECS is an open source project and we love to receive contributions from our comm
 
 ## Table of Contents
 
-- [How to Contribute](#how-to-contribute)
+- [How to contribute](#how-to-contribute)
+- - [Special guidance during OTel donation of ECS](#special-guidance-during-otel-donation-of-ecs)
  - [Dev Tools](#dev-tools)
  - [Submitting Changes](#submitting-changes)
 - [Git and Github Guidelines](#git-and-github-guidelines)
@@ -22,12 +23,58 @@ ECS is an open source project and we love to receive contributions from our comm
 - [Schema Files](#schema-files)
 - [Additional Resources](#additional-resources)
 
-## How to Contribute
 
-There are two primary ways in which you can contribute to ECS.
+## How to contribute
 
-1. The [RFC process](./rfcs/README.md) is used for significant additions or breaking changes to the schema itself.
-2. For bug fixes or incremental, non-controversial additions to ECS, changes can be made directly to the ECS project and submitted as pull request.
+## ECS Donation to OpenTelemetry
+In April 2023, OpenTelemetry and Elastic made an [important joint announcement](https://opentelemetry.io/blog/2023/ecs-otel-semconv-convergence/). In this announcement Elastic
+shared its intention to achieve convergence of ECS and OTel Semantic Conventions into a single standard maintained
+by OpenTelemetry.
+
+The stated plan has been to keep ECS in a frozen state during the transition. However, it is also apparent that these
+things take time. It takes time for the OTel community to adopt donated fields, and it will take time for development
+teams to build OTel native constructs in the Elastic stack. In the meantime, ECS users need to be able to develop
+features for Elastic that rely on continued contributions to the schemas that drive our technology.
+
+For these reasons, we need a process and guidelines for contributing to these data schemas during this period that
+allows us to avoid breaking changes.
+
+### How to contribute during OTel donation of ECS
+
+Bug fixes or minor field addition changes can be made directly to the ECS project and submitted as pull requests.
+
+Significant changes that add new use cases, top-level fieldsets, or could be considered controversial are
+considered material. The general rule for contributing new material changes to schemas during the transition period is
+
+- First, merge a pull request to
+[OTel Semantic Conventions](https://github.com/open-telemetry/semantic-conventions/blob/main/CONTRIBUTING.md) with new
+fields, namespaces or schemas
+- Second, to backport those changes to ECS at the starting point indicated in the table below
+- Finally, once the Semantic Conventions changes are marked as stable, remove the Beta designation in ECS
+
+This will ensure that the latest changes are included in OTel Semantic Conventions, where schema evolution will continue
+as the merger proceeds. It will also allow teams and users to continue using ECS while OTel migration tools and guidance
+are being developed. Finally, this will reduce the risk of breaking changes if new fields are merged first to ECS, and
+then require changes before being adopted in Semantic Conventions.
+
+_There are some exceptions to this rule._
+
+1. My contribution to OTel Semantic Conventions is stalled. We are waiting for a sign-off from a second company.
+In the meantime, our Elastic feature is blocked.
+2. I want to build a workflow in Elastic, and the fields I need to proceed are already in OTel but not in ECS where I
+need them today.
+
+In these cases, the recommendation is to make a contribution to ECS to unblock development. The appropriate ECS starting
+point can be an [RFC](./rfcs/README.md) or pull request based on the maturity of the Otel changes. Please see the
+following table.
+
+| OTel submission maturity | Breaking changes expected | ECS starting point |
+|--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|---------------------------|------------------------------------------------------|
+| OTel working groups accepts the premise of the addition and commits to considering this proposal as it advances. | Major | RFC Stage 1 |
+| The initial field definitions comprehensively model the addition to the schema. Fundamental questions and concerns are resolved, though some less significant questions remain open. | Iterative | RFC Stage 2 |
+| All requested changes from codeowners have been addressed, and there are no open discussions. | Iterative | Open an ECS pull request with new fields marked Beta |
+| Fields, schema, namespace exists in OTel and are designated experimental | Iterative | Open an ECS pull request with new fields marked Beta |
+| Fields, schema, namespace exists in OTel and are designated stable | None | Open an ECS pull request with new fields marked GA |
 
 ### Dev Tools
 

README.md

@@ -9,9 +9,18 @@ ingesting data into Elasticsearch. A common schema helps you correlate
 data from sources like logs and metrics or IT operations
 analytics and security analytics.
 
+## ECS Donation to OpenTelemetry
+In April 2023, OpenTelemetry and Elastic made an
+[important joint announcement](https://opentelemetry.io/blog/2023/ecs-otel-semconv-convergence/).
+In this announcement, we shared our intention to achieve convergence of ECS and OTel
+Semantic Conventions into a single standard maintained by OpenTelemetry.
+
+Special guidance is provided during the donation period. Please review the [contribution guide](CONTRIBUTING.md).
+
 ## Documentation
 
 The ECS reference is published on the main Elastic documentation website.
+
 Visit [the official ECS Reference Documentation](https://www.elastic.co/guide/en/ecs/current/index.html).
 
 ## Getting Started