Include jekyll generation into the deploy script

Run jekyll --no-server --no-auto so the _site/ is automatically
generated
Update README

Add information about the git branching workflow.
Update post.date and post.description displays

Customize .island and .islet
Reduce post.date size and go back to a newline
Reduce the number of post per page
Display the post.description at the beginning of the post
First EN post - How to build a multilingual Jekyll blog
First FR post - Faire son blog avec Jekyll
Delete test posts (don't need them anymore)