Add a roles page draft
Minor typofixes
Hint at dual roles

As suggested by @floord and @berlintam
add sponsors and coaching companies roles
Merge branch 'sf-add-roles-page' of github.com:rails-girls-summer-of-code/summer-of-code into sf-add-roles-page
fix permalink for roles
updated text and formatting
Merge pull request #166 from rails-girls-summer-of-code/sf-add-roles-page

Add a roles page