Pedantic rewording of why relative importing doesn't work in main modules (pythonGH-136846)

Pedantically reword the section about relative imports and main modules.

Author: thejcannon

Doc/tutorial/modules.rst

@@ -579,8 +579,8 @@ module for example, you might use::
    from .. import formats
    from ..filters import equalizer
 
-Note that relative imports are based on the name of the current module.  Since
-the name of the main module is always ``"__main__"``, modules intended for use
+Note that relative imports are based on the name of the current module's package.
+Since the main module does not have a package, modules intended for use
 as the main module of a Python application must always use absolute imports.