Update README
Fix a typo
Prepend bundle exec to middleman command
Use link_to_lang helper
Use relative path for links
Append solidus to links to directory index
Update Bundler
Install Webrick
Add Webrick to dependencies
Remove Crowdin related code from template
Co-authored-by: Kitaiti Makoto <KitaitiMakoto@gmail.com>
Reviewed-on: plume/documentation#113
