Outdated former version of a developer guide for mulle-objc.

Superseded by this version of De Re mulle-objc

bundle exec jekyll serve -d /tmp/_site

or use mulle-dockerize and just say:

jekyll serve -d /tmp/_site

Update packages with sudo bundle update.

Check https://stackoverflow.com/questions/46377667/docker-for-mac-mkmf-rb-cant-find-header-files-for-ruby if you run into problems with missing ruby headers.