add docs about "npm install" and running specific versions
add docs about "npm install" and running specific versions

mwest1066/PrairieLearn,jakebailey/PrairieLearn,parasgithub/PrairieLearn,mwest1066/PrairieLearn,jakebailey/PrairieLearn,rbessick5/PrairieLearn,parasgithub/PrairieLearn,rbessick5/PrairieLearn,parasgithub/PrairieLearn,jakebailey/PrairieLearn,tbretl/PrairieLearn,mwest1066/PrairieLearn,mwest1066/PrairieLearn,rbessick5/PrairieLearn,jakebailey/PrairieLearn,mwest1066/PrairieLearn,rbessick5/PrairieLearn,tbretl/PrairieLearn,parasgithub/PrairieLearn,tbretl/PrairieLearn,parasgithub/PrairieLearn,rbessick5/PrairieLearn,tbretl/PrairieLearn,tbretl/PrairieLearn