The folder contains the required files to create a docset which can be used in documentation browsers like Dash, Velocity, or Zeal.
The docset can be created with
make JSON_for_Modern_C++.docset
The generated folder JSON_for_Modern_C++.docset can then be opened in the documentation browser. make all builds a JSON_for_Modern_C++.tgz archive instead, and make install_docset_zeal installs the docset for Zeal directly.
A recent version is also part of the Dash user contributions.
The JSON logo is public domain.