CONTRIBUTING.md: Change 'clone' to 'fork' for GitHub duping

This is the lingo that GitHub uses, and for me the instructions read
more clearly with a local clone and a remote fork.
Merge pull request #269 from gvwilson/master

Fixing EventBrite registration on various pages
Moved January 31 bootcamp to list of previous bootcamps
Added check-bare to the Makefile for doing an unvalidated build
Merge pull request #267 from wking/blog-contrib

CONTRIBUTING.md: Change 'clone' to 'fork' for GitHub duping
Merge pull request #270 from pipitone/make-check-bare

Added check-bare to the Makefile for doing an unvalidated build
Merge pull request #271 from gvwilson/master

Restoring material about GEOMAR lost during a merge...
Merge pull request #272 from gvwilson/master

Blog post about Next Generation Sequencing course