add an appendix for internal communication: how raw data from CodeParrot processed from beginning to the end

[chunhualiao]

using a few concrete examples.

[bin123apple]

Just uploaded a log file data/processing.log, which contains three concrete examples.

They record how the raw CodeParrot fortran code is processed to fortran-cpp data pairs.

• dataset generation pipeline: from github Fortran code to Fortran vs. C++ data pairs