readFile refers to a fully buffered process in which a response is only returned
when the complete file is pushed into the buffer and read.
In contrast, createReadStream refers to a process only partly buffered and is treated
as an event series with the whole file split into chunks, processed, and then sent back as a response one after the other.
readFile is a more memory-intensive process and can be slow, especially with large files, whereas createReadStream is faster for processing large files.