Add note to README about weird breadcrumbs.
Fixing three bugs filed against the "writing a transformer" docs.

BUG=
R=nweiz@google.com

Review URL: https://codereview.appspot.com/98300044
Fixing broken links.

BUG=

Review URL: https://codereview.appspot.com/92550045
Early preview of the Observatory docs.

BUG=
R=johnmccutchan@google.com, kathyw@google.com

Review URL: https://codereview.appspot.com/91220043