Document Javelin behaviors
Document Javelin behaviors

Summary: Provide a concept document for Javelin behaviors which explains what they are and how they fit into the grand scheme.

Test Plan: Read the document. Hit up the sweet example.

Reviewers: cpojer, tomo, mroch

CC:

phacility/javelin,phacility/javelin,phacility/javelin,phacility/javelin,phacility/javelin