Update third-party.md

Added my version of ngauthier's importrb. Its a more basic approach that ignores comments and other types like pages, templates, etc. But it takes another step to turn posts into markdown files instead of html files.
Merge branch 'patch-1' of https://github.com/dseeman/jekyll-import into dseeman-patch-1

* 'patch-1' of https://github.com/dseeman/jekyll-import:
  Update third-party.md
Update with what @dseeman said.