<div class="form-group">
  <%= f.label :country %>
  <%= f.select :country, facet_options(f, :country), { include_blank: true }, { class: 'form-control' } %>
</div>

<div class="form-group">
  <%= f.label :country %>
  <%=
    f.select :country, facet_options(f, :country),
      { include_blank: true },
      { class: 'select2', multiple: true, data: { placeholder: 'Select countries' } }
  %>
</div>

Allow multi-selection of DFID countries
Allow multi-selection of DFID countries

DFID need to be able to apply more than one country to a research
output. This is not, as we thought, a function of the schema JSON.

It requires us to specify our own select2 box that copes with multiples.
The approach is lifted from the original specialist-publisher:

https://github.com/alphagov/specialist-publisher/commit/2fd6b482a5dde0ac9d55f7f9bbff015ad7bcdd4c#diff-f6f8d3c9d3b4dcf7b1200f17714d0e95R9
