docs: Add guidelines for handling serial PR dependencies

Clarify the process for managing and reviewing pull requests with serial
dependencies. This helps contributors understand how to structure,
propagate changes, and validate dependent PRs effectively.

Signed-off-by: Abderrahmane JARMOUNI <[email protected]>

Author: JarmouniA

doc/contribute/contributor_expectations.rst

@@ -200,6 +200,34 @@ request that they create an :ref:`RFC proposal <rfcs>`.
 
 .. _`Codecov`: https://app.codecov.io/gh/zephyrproject-rtos/zephyr
 
+Handling Serial Dependency Between PRs
+======================================
+
+When PRs have serial dependencies, e.g. PR C depends on PR B, which depends on PR A,
+follow this process to ensure code compiles and tests pass at each stage:
+
+- Submit All PRs Together
+
+   - Open PRs A, B, and C simultaneously.
+   - Mark only PR A as "Ready for Review."
+
+- Include Dependencies in Each PR
+
+   - In PR B, include the commits from PR A.
+   - In PR C, include the commits from both PR A and PR B.
+
+- Propagate Changes
+
+   Any updates to PR A must be manually propagated to PR B, and then from PR B to PR C.
+   This ensures PR C always reflects the latest state of all dependencies.
+
+- Review and Merge Process
+
+   PR A will be reviewed first. PR C’s tests (either in-tree ones or newly added) are used
+   to validate the combined functionality of A, B, and C.
+   Once PR A is merged, repeat the process for PR B (mark it as "Ready for Review" and use
+   PR C for validation).
+
 Workflow Suggestions That Help Reviewers
 ========================================