1. Run xcode-select –install first
  2. Run brew install graphviz
  3. Run mkdir /usr/local/Frameworks if the following errors occur:

Error: An unexpected error occurred during the `brew link` step
The formula built, but is not symlinked into /usr/local
Permission denied @ dir_s_mkdir – /usr/local/Frameworks
Error: Permission denied @ dir_s_mkdir – /usr/local/Frameworks