add complete documentation

Hey.

It would be nice if there was something like a write_to_stdout() function, or if write_to_textfile() would somehow allow writing to stdout.

For debugging that would seem to be much more helpful. Also, distros may have their own unified means of collecting the .prom files and thus even in production it may make sense to let a program simply write the metrics to stdout.

Cheers,
Chris.

PS: Using /dev/stdout doesn't work, as it tries to write it's tmpfile there.

Comience localizando write_to_textfile() y revisando cómo maneja el caso /dev/stdout. Determine el comportamiento esperado al escribir métricas directamente en stdout, conservando la salida existente a archivos, y verifique después que ambas rutas de salida funcionen según lo previsto. En el issue no se nombran archivos ni pruebas.