[CE-423] Update the contribution doc

Developer can add `CE-1234 #done` at commit msg, to trigger the
jira issue to close automatically after the commit is merged.

CE-423 #done.

Change-Id: I2c6e7da5c59cdc0fd1295b389eb163ba41a3007b
Signed-off-by: Baohua Yang <yangbaohua@gmail.com>

docs/CONTRIBUTING.md

@@ -69,15 +69,15 @@ $ make check
 $ git commit -s -a
 ```
 
-Example commit msg may look like:
+Example commit msg may look like (take CE-1234 for example):
 
 ```sh
-[CE-26] A short description of your change with no period at the end
+[CE-1234] A short description of your change with no period at the end
 
 You can add more details here in several paragraphs, but please keep each line
 width less than 80 characters. A bug fix should include the issue number.
 
-Fix https://jira.hyperledger.org/browse/CE-26.
+CE-1234 #done.
 
 Change-Id: If2e142ea1a21bc4b42f702f9a27d70d31edff20d
 Signed-off-by: Your Name <committer@email.address>
@@ -104,4 +104,4 @@ After the ci checking passed, add [reviewers](https://wiki.hyperledger.org/proje
 
 * If you need to refine the patch further as the reviewers may suggest, you can change on the same branch, and commit the new code with `git commit -a --amend`, and then use the `git review` command again.
 
-<a rel="license" href="http://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by/4.0/88x31.png" /></a><br />This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.
+<a rel="license" href="http://creativecommons.org/licenses/by/4.0/"><img alt="Creative Commons License" style="border-width:0" src="https://i.creativecommons.org/l/by/4.0/88x31.png" /></a><br />This work is licensed under a <a rel="license" href="http://creativecommons.org/licenses/by/4.0/">Creative Commons Attribution 4.0 International License</a>.