Update header.html

clean
Update header.html

change description
Update header.html

add contributors
Update header.html

add keywords
Update default.html

bump default header provide by jekyll
Update _config.yml

add permalink: pretty
Update default.html

include nav-main.html
Add nav-main to includes

with scaffold
Add about-blocks section

with scaffold
Add about-css section

with scaffold
Add como-usar section

with scaffold
Add navbar styles