Add `/.editorconfig`

## See: http://editorconfig.org/
> .gitattributes make it the default for boilerplate projects.

@SBoudrias I apologize for not being clear. What I meant is that people (and also other projects) may decide to only keep / include certain files from the boilerplate, and thus, the usage of Git and/or the inclusion of the `.gitattributes` file is not guaranteed.