add URLs to Classroom index page
add URLs to Classroom index page

The headers for each subsection now link to each corresponding index page.
hardikjain29/docs,katieporter/docs,hardikjain29/docs,Whatthefoxsays/docs,Zaftula/docs,hardikjain29/docs,Whatthefoxsays/docs,Aonepathan/docs,Zaftula/docs,sendgrid/docs,Whatthefoxsays/docs,Aonepathan/docs,hardikjain29/docs,katieporter/docs,hardikjain29/docs,Aonepathan/docs,Aonepathan/docs,Zaftula/docs,Zaftula/docs,ksigler7/docs,katieporter/docs,ksigler7/docs,Aonepathan/docs,katieporter/docs,jacobmovingfwd/docs,jacobmovingfwd/docs,sendgrid/docs,jacobmovingfwd/docs,katieporter/docs,sendgrid/docs,Zaftula/docs,jacobmovingfwd/docs,jacobmovingfwd/docs,ksigler7/docs