Improve clarification about communication methods in episode 3 (#50)

* improve clarification between communication modes

* re-arrange episode to improve flow into communication modes and following section

* change structure of lesson to flow with the new blocking vs. non-blocking section

* remove submodule folder

* add callout to explain that bsend is not non-blocking

* one last fix for grammar and spelling mistakes

* Delete .gitmodules

* Apply suggestions from code review for 05-collective-communication

Co-authored-by: Steve Crouch <[email protected]>

* address review comments

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Co-authored-by: Steve Crouch <[email protected]>