Add docs
- List, Loader, Rail, Reveal.

Signed-off-by: Lee <jessy1092@gmail.com>
Fix Segment bug: add color attribute.
- Add Docs: Segment.

Signed-off-by: Lee <jessy1092@gmail.com>
Add Docs: Steps/Step.

Signed-off-by: Lee <jessy1092@gmail.com>