Create project collaboration guide

[toshify]

Create project collaboration guide page with process description, license/collaborator agreement, glossary etc.

Terminology
lesson - collection of items to exercise
(lesson) item - a word and its corresponding meta data, like audio
(exercise) session - a sequence of exercises
exercise - an exercise template populated with a lesson item presented as an interactive exercise for the user to solve and thereby increase retention of knowledge of the lesson item
exercise template - a template for practicing a lesson item, like the multiple-choice exercise template
item(s) under test - the particular item(s) from a lesson that is/are the focus of a particular exercise
home screen - lessons list
bottom navigation bar - nav bar

[toshify]

CONTRIBUTING.md contains most of the current information on collaboration, but should probably be reviewed for simplicity and updated to current practice.
Project management information is lacking (see issue #400).