Add reviewer guidelines (#2966)

Co-authored-by: Armin Ruech <[email protected]>

Author: lmolkova

CONTRIBUTING.md

@@ -27,6 +27,7 @@ requirements and recommendations.
       - [Examples](#examples)
     - [Adding a changelog entry](#adding-a-changelog-entry)
   - [5. Getting your PR merged](#5-getting-your-pr-merged)
+- [Reviewer guidelines](#reviewer-guidelines)
 - [Automation](#automation)
   - [Consistency checks](#consistency-checks)
   - [Auto formatting](#auto-formatting)
@@ -287,10 +288,9 @@ Alternately, copy `./.chloggen/TEMPLATE.yaml`, or just create your file from scr
 
 A PR (pull request) is considered to be **ready to merge** when:
 
-- It has received at least two approvals from the [code
-  owners](./.github/CODEOWNERS) (if approvals are from only one company, they
-  won't count)
-- There is no `request changes` from the [code owners](./.github/CODEOWNERS)
+- It has received at least two approvals from the [code owners](./.github/CODEOWNERS)
+- There is no `request changes` from the [code owners](./.github/CODEOWNERS) for
+  affected area(s)
 - There is no open discussions
 - It has been at least two working days since the last modification (except for
   the trivial updates, such like typo, cosmetic, rebase, etc.). This gives
@@ -301,6 +301,35 @@ A PR (pull request) is considered to be **ready to merge** when:
 Any [maintainer](./README.md#contributing) can merge the PR once it is **ready
 to merge**.
 
+## Reviewer guidelines
+
+Semantic conventions consist of multiple [areas](./AREAS.md) with ownership
+defined in the [CODEOWNERS](./.github/CODEOWNERS) file.
+
+When a PR is raised against specific area(s), it is recommended to allow the corresponding
+area(s) owners to review and iterate on it first before approving or rejecting the PR.
+
+A review from [@specs-semconv-approvers](https://github.com/orgs/open-telemetry/teams/specs-semconv-approvers)
+is required on every PR and, in most cases, follows after area(s) owners approval.
+
+Before merging a PR, [@specs-semconv-maintainers](https://github.com/orgs/open-telemetry/teams/specs-semconv-maintainers)
+MUST verify that the PR has been approved by the corresponding area owner(s). For
+non-trivial changes, maintainers SHOULD NOT merge PRs without other code owner approvals.
+
+Reviews from non-code owners are encouraged, with the following assumptions:
+
+- There is a reasonable intersection between the change and the reviewer's area of expertise or interest
+- Area owners have autonomy to accept or dismiss feedback from non-codeowners and
+  SHOULD consult with [@specs-semconv-maintainers](https://github.com/orgs/open-telemetry/teams/specs-semconv-maintainers)
+  in case of conflicts
+
+When reviewing changes, reviewers SHOULD include relevant context such as:
+
+- Links to documentation related to the technology in question
+- Links to applicable semantic conventions or OpenTelemetry guidelines
+- Links to relevant PRs, issues, or discussions
+- Reasons for suggesting the change
+
 ## Automation
 
 Semantic Conventions provides a set of automated tools for general development.