This commit adds a descriptive comment at the beginning of the `mrb_read_float` function in `src/readfloat.c`.
The comment explains the function's purpose, its parameters (`str`, `endp`, `fp`), and its return value (`TRUE` or `FALSE`). This improves code readability and understanding.
The new version gives more accurate values for decimal number
representation that are not divisible in binary representations, for
example `0.3`.
The function uses `long double` for precision. Please report if `long
double` causes problems on any platform (especially microcontrollers).
Ref #6182