Example C code needs a comment

[davidmalcolm]

https://gcc-newbies-guide.readthedocs.io/en/latest/inside-cc1.html#how-does-cc1-turn-c-into-assembler

I got some feedback that the C example distracted a reader.

Needs a leading comment along the lines of "this is just a meaningless example of a C function, just something to demonstrate a conditional and some nested arithmetic expressions"