NextGen_Core.rst: Add link to IO docs
NextGen_Core.rst: Add link to IO docs

coala/coala,jayvdb/coala,coala/coala,SanketDG/coala,jayvdb/coala,coala-analyzer/coala,SanketDG/coala,coala/coala,SanketDG/coala,jayvdb/coala,coala-analyzer/coala,coala-analyzer/coala