I want to know if including a file summary comment at the beginning of each file is a good way of knowing what each file does or is there a better way.
A high-level summary comment at the beginning of any code unit like a module, class or package, explaining the purpose and/or responsibilities of the unit is definitely a useful way of commenting in almost any programming language I know. In many languages, it is not uncommon (and in some cases like Java it is even mandatory) to have a 1:1 correspondence between code files and such code units, and there the answer is IMHO "yes, absolutely".
However, I recommend you better use a mental model of summary comments per logical unit, not per physical (file) unit, this will often make more sense. Be aware that lots of programming languages allow multiple units per file, or have certain conventions to distribute one unit over a number of files (for example, splitting a C++ class into a header and an implementation file).