Add documentation about analytics

[D3AH]

Now is no information in the page about what is send with analytics enabled.

We should add this info https://github.com/ember-cli/ember-cli/blob/master/docs/analytics.md in the Appendix section.

[jenweber]

This issue is still relevant and would be good for someone to write!

To do:

• Add a new page to the Appendix called Analytics
• Be sure to include the new page name in pages.yml
• Include the content from the page D3AH linked to
• Write an introduction explaining what these are and when to use them

[arafatiqbal]

I'm going to work on this if nobody has taken this on!

[jenweber]

Thank you, that would be great!