Improve Chrome OS VPN API documentation

Improve Chrome OS VPN API documentation

Clarify that packets originating on Chrome OS are intercepted by the API,
not packets reaching the device from outside.

BUG=407541
Committed: https://crrev.com/b75aff40c818606e554617fb8323b4a696e3e899
Cr-Commit-Position: refs/heads/master@{#311509}

[bartfab (slow), 2014-12-16 14:02:54]

bartfab@chromium.org changed reviewers:
+ mkearney@chromium.org

[bartfab (slow), 2014-12-16 14:02:54]

Hi Margaret,

Could you take a look please?

[bartfab (slow), 2015-01-08 17:10:08]

On 2014/12/16 14:02:54, bartfab wrote:
> Hi Margaret,
> 
> Could you take a look please?

Hi Margaret,

Friendly review ping.

[mkearney1, 2015-01-14 17:15:46]

lgtm

[bartfab (slow), 2015-01-14 17:16:11]

The CQ bit was checked by bartfab@chromium.org

[commit-bot: I haz the power, 2015-01-14 17:16:53]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/804363002/1

[commit-bot: I haz the power, 2015-01-14 18:06:37]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-01-14 18:09:42]

Patchset 1 (id:??) landed as
https://crrev.com/b75aff40c818606e554617fb8323b4a696e3e899
Cr-Commit-Position: refs/heads/master@{#311509}