Improve links to CI examples

Report https://news.ycombinator.com/item?id=11092090

I found the CI examples are hard to find, suggestions:

• Rename http://doc.gitlab.com/ce/ci/languages/php.html to http://doc.gitlab.com/ce/ci/examples/php.html
• Create an examples page in the ci documentation (http://doc.gitlab.com/ce/ci/exmaples/) that has a link to http://doc.gitlab.com/ce/ci/examples/php.html and all others
• Change the link at the bottom of http://doc.gitlab.com/ce/ci/quick_start/README.html to point to that page
• Add the examples section 'CI Examples' higher on http://doc.gitlab.com/ce/
• Add a link to the examples page to http://doc.gitlab.com/ce/ci/yaml/README.html