Python: Expand __main__.py comment

Co-authored-by: Rasmus Wriedt Larsen <[email protected]>

Author: tausbn

python/ql/src/semmle/python/Files.qll

@@ -92,6 +92,11 @@ class File extends Container {
       ) and
       // Exclude files named `__main__.py`. These are often _not_ meant to be run directly, but
       // contain this construct anyway.
+      //
+      // Their presence in a package (say, `foo`) means one can execute the package directly using
+      // `python -m foo` (which will run the `foo/__main__.py` file). Since being an entry point for
+      // execution means treating imports as absolute, this causes trouble, since when run with
+      // `python -m`, the interpreter uses the usual package semantics.
       not this.getShortName() = "__main__.py"
       or
       // The file contains a `#!` line referencing the python interpreter