jekyll: add Gemfile for gitub-pages bundler.

* Gemfile: New file.  Run `bundle install` or `bundle update
github-pages` to run jekyll locally.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>
markdown: insert missing quote.

* index.md: Insert missing quote mark.

Signed-off-by: Gary V. Vaughan <gary@gnu.org>