add default thumbnail pictogram
use file thumbnail helper for sites
Update README.md

little typo: scss.css --> css.scss
Update README.md

Link to trouble shooting page and small typo fixes.
Update README.md

Fix issues link.
Require Pageflow 0.5 or higher

`file_thumbnail_css_class` helper is not available in earlier
versions.
Merge pull request #2 from tf/thumbnails

Thumbnails
Merge pull request #1 from kerygmafabian/patch-1

Update README.md
bump version to 0.1.0
fix links Fix links in Changelog