Improve documentation

[Johan Pretorius]

This page shows how to create the gh-pages branch better.

https://help.github.com/articles/creating-project-pages-manually/#create-a-gh-pages-branch

Use

cd repository

git checkout --orphan gh-pages
# Creates our branch, without any parents (it's an orphan!)
# Switched to a new branch 'gh-pages'

git rm -rf .
# Remove all files from the old working tree
# rm '.gitignore'

instead of what is shown here.

Also say that the

site.includeScaladoc()

is required even if your sbt project is java only.