CONTRIBUTING.md: Add Eclipse ECA chapter

This chapter was copied from jakarta project with minor fix

Relate-to: eclipse/oniro-core/docs#96
Forwarded: eclipse/oniro-core/oniro!105


Signed-off-by: Philippe Coval <philippe.coval.ext@huawei.com>

CONTRIBUTING.md

@@ -16,6 +16,7 @@ SPDX-License-Identifier: CC-BY-4.0
     -   [Overview](#overview-1)
     -   [Developer Certificate of Origin](#developer-certificate-of-origin)
 -   [`oniro`-specific contributions process and guidelines](#oniro-specific-contributions-process-and-guidelines)
+-   [Eclipse Contributor Agreement](#eclipse-contributor-agreement)
 
 # Gitlab Contributions
 
@@ -215,3 +216,14 @@ Signed-off-by: Joe Developer <joe.developer@example.com>
 
 Please note that by signing off the commit, you make a **legally binding
 statement** that you certify as in the [DCO sign-off](#dco-sign-off) section.
+
+# Eclipse Contributor Agreement
+
+Before your contribution can be accepted by the project team, contributors must electronically sign the
+[Eclipse Contributor Agreement (ECA)](http://www.eclipse.org/legal/ECA.php)
+
+Commits that are provided by non-committers must have a Signed-off-by field in the footer indicating that the author is aware of the terms by which the contribution has been provided to the project.
+The non-committer must additionally have an Eclipse Foundation account and must have a signed Eclipse Contributor Agreement (ECA) on file.
+
+For more information, please see the [Eclipse Committer Handbook](https://www.eclipse.org/projects/handbook/#resources-commit)
+