How to find out the correct scope (selector)

Added findings from https://discuss.atom.io/t/how-do-you-configure-use-snippets/335/28
This should probably be an ordered list, since it is a step-by-step.

Also, do you think it would be easier to tell people that the scope for a given language is in the Settings View? For example, for HTML:

![scope](https://cloud.githubusercontent.com/assets/1038121/5137632/126beb66-70f2-11e4-839b-bc7e84103f67.png)