Update documentation of how to use roll-dep in DEPS file.

Update documentation of how to use roll-dep in DEPS file.

The roll-dep script no longer deals with SVN revisions and now just rolls to the
latest origin/master.

NOTRY as this is just comments in DEPS.

BUG=
NOTRY=true

Committed: https://crrev.com/1859920b5a924f856b2be9174c95b0d58b7bcdcf
Cr-Commit-Position: refs/heads/master@{#342815}

[Andrew Hayden (chromium.org), 2015-08-11 11:29:05]

andrewhayden@chromium.org changed reviewers:
+ tandrii@chromium.org

[Andrew Hayden (chromium.org), 2015-08-11 11:29:13]

Minor cleanup, PTAL.

[tandrii(chromium), 2015-08-11 11:33:49]

Since you wrote original piece, LGTM :)

[Andrew Hayden (chromium.org), 2015-08-11 13:05:44]

The CQ bit was checked by andrewhayden@chromium.org

[commit-bot: I haz the power, 2015-08-11 13:05:51]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1289473002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1289473002/1

[commit-bot: I haz the power, 2015-08-11 13:13:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-08-11 13:14:11]

Patchset 1 (id:??) landed as
https://crrev.com/1859920b5a924f856b2be9174c95b0d58b7bcdcf
Cr-Commit-Position: refs/heads/master@{#342815}