Update Gruntfile.js

use docs/theme.less -> themes/docs.less in compileDocs
[docs] Add src/less/themes/docs/theme.less

use this -> themes/docs.less
[docs] Add src/less/themes/docs/styles.less

with initial styles
[docs] Increase _includes/sections/home.html

add how-to-use button and initial description
0.0.37