Update CONTRIBUTING.md, test CQ

Update CONTRIBUTING.md, test CQ

BUG=531547
Committed: https://github.com/GoogleChrome/custom-tabs-client/commit/41ded9d4b5dbaf7b79e291ee8a222f5efbc52190

[pasko, 2015-09-29 08:19:28]

pasko@chromium.org changed reviewers:
+ lizeb@chromium.org

[pasko, 2015-09-29 08:19:40]

please take a look

[Benoit L, 2015-09-29 08:22:29]

lgtm

[pasko, 2015-09-29 09:39:10]

The CQ bit was checked by pasko@chromium.org

[commit-bot: I haz the power, 2015-09-29 09:39:15]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1377773003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1377773003/1

[commit-bot: I haz the power, 2015-09-29 11:39:24]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-09-29 11:39:25]

Try jobs failed on following builders:
  Custom Tabs Linux Tryserver on master.tryserver.client.custom_tabs_client
(JOB_TIMED_OUT, no build URL)

[pasko, 2015-09-30 19:28:49]

The CQ bit was checked by pasko@chromium.org

[commit-bot: I haz the power, 2015-09-30 19:29:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1377773003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1377773003/1

[commit-bot: I haz the power, 2015-09-30 19:29:53]

Committed patchset #1 (id:1) as
https://github.com/GoogleChrome/custom-tabs-client/commit/41ded9d4b5dbaf7b79e...