add comments to use C4 as learning resources

[coolharsh55]

Through the use of comments to describe the structure and interpretation of a C program, C4 can be turned into a learning resource for those who wish to learn C/compilers.

[ebraminio]

I found https://github.com/lotabout/write-a-C-interpreter quite useful in this regard.

[Hanseltu]

Awesome!!!

[AoiKuiyuyou]

Added line-by-line comments to rswier/c4's c4.c in AoikC4Study. Added line-by-line comments to EarlGray/c4's c4.c and c4x86.c in AoikC4x86Study. Sent a pull request.