Try again to fix the links in the GN README.md.

Try again to fix the links in the GN README.md.

Turns out that gitiles is even more broken than I thought, and
using absolute paths for links doesn't work either. This patch
changes the links in GN's README.md to use full URLs instead.

TBR=nodir@chromium.org
BUG=

Committed: https://crrev.com/c8bcd19882e5f0ba62badf0ebd2efde625531c7e
Cr-Commit-Position: refs/heads/master@{#353682}

[Dirk Pranke, 2015-10-13 04:54:14]

The CQ bit was checked by dpranke@chromium.org

[commit-bot: I haz the power, 2015-10-13 04:54:45]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1394433004/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1394433004/1

[commit-bot: I haz the power, 2015-10-13 05:06:33]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-13 05:07:33]

Patchset 1 (id:??) landed as
https://crrev.com/c8bcd19882e5f0ba62badf0ebd2efde625531c7e
Cr-Commit-Position: refs/heads/master@{#353682}

[tfarina, 2015-10-13 05:14:13]

tfarina@chromium.org changed reviewers:
+ tfarina@chromium.org

[tfarina, 2015-10-13 05:14:13]

lgtm