add README link to 'Contributing' blog post
add README link to 'Contributing' blog post

PrairieLearn/PrairieLearnHack,jakebailey/PrairieLearn,PrairieLearn/PrairieLearnHack,rbessick5/PrairieLearn,kevinwang/PrairieLearn,kevinwang/PrairieLearn,rbessick5/PrairieLearn,parasgithub/PrairieLearn,tbretl/PrairieLearn,mwest1066/PrairieLearn,kevinwang/PrairieLearn,lotrfan/PrairieLearn,parasgithub/PrairieLearn,lotrfan/PrairieLearn,mwest1066/PrairieLearn,rbessick5/PrairieLearn,PrairieLearn/PrairieLearnHack,kevinwang/PrairieLearn,tbretl/PrairieLearn,mwest1066/PrairieLearn,jakebailey/PrairieLearn,jakebailey/PrairieLearn,mwest1066/PrairieLearn,lotrfan/PrairieLearn,parasgithub/PrairieLearn,mwest1066/PrairieLearn,kevinwang/PrairieLearn,kevinwang/PrairieLearn,tbretl/PrairieLearn,PrairieLearn/PrairieLearnHack,kevinwang/PrairieLearn,tbretl/PrairieLearn,PrairieLearn/PrairieLearnHack,tbretl/PrairieLearn,jakebailey/PrairieLearn,rbessick5/PrairieLearn,parasgithub/PrairieLearn,PrairieLearn/PrairieLearnHack,lotrfan/PrairieLearn,lotrfan/PrairieLearn,PrairieLearn/PrairieLearnHack,PrairieLearn/PrairieLearnHack,lotrfan/PrairieLearn,rbessick5/PrairieLearn,parasgithub/PrairieLearn,lotrfan/PrairieLearn