Initial commit for always cohort inline discussions plus spelling fix

Moved from original branch on edx-platform repo to edx-documentation repo
I agree with @lamagnifica 's comments. I think this would be clearer if you said "If you want general topics to be divided, do some stuff" and "if you want inline topics to be divided, you don't need to do some stuff. To unify inline topics, do some stuff." 

Also agree that "perform" causes issues with translation.