add updated knitr code
add updated knitr code

mjones01/NEON-Data-Skills,NEONScience/NEON-Data-Skills,mjones01/NEON-Data-Skills,NEONScience/NEON-Data-Skills,NEONScience/NEON-Data-Skills,NEONScience/NEON-Data-Skills,mjones01/NEON-Data-Skills