added about the discussion stage to the LC description

[fix carpentries/styles#311] update descriptions of the carpentries

Pull Request: carpentries/styles#313

Check that Rmd episode files include `source: Rmd`

Fixes carpentries/styles#273

links.md: add links to carpentries' lessons overview pages

* Add 'cp' (Carpentry) as a lesson type (for instructor training)
* Explain lesson type abbreviations (swc, dc, lc, cp)
* Emphasize the fact that there is no need to edit "repository" variable in front matter

update URLs to reflect consolidation to carpentries organization

Add links.md to files in boilerplate

Makefile: add docker-serve target

Move CODE_OF_CONDUCT.md to boilerplate

remove permalink that breaks asset includes

gitIgnore for R

Closes swcarpentry/styles#283

`site.email` is used as:

_includes/lesson_footer.html:	        <a href="mailto:{{ site.email }}">Contact</a>
_includes/workshop_footer.html:	<a href="mailto:{{ site.email }}">Contact</a>

Therefore, it does not make sense to have `mailto` in the `email` itself.

Will also match https://raw.githubusercontent.com/swcarpentry/lesson-example/gh-pages/CONDUCT.md

Rename CoC file to align with GitHub's Community Profile expectation

See https://help.github.com/articles/about-community-profiles-for-public-repositories/.

Fix lesson_check.py