Add gitbook-plugin-edit-link

[olasitarska]

More information: http://plugins.gitbook.com/plugin/edit-link

Could be easier for readers to fix the bugs they see in the tutorial.

[aniav]

This plugin currently doesn't work with multilanguage books. I have created a pull request to add it:
rtCamp/gitbook-plugin-edit-link#2

We will have to wait for it :)