Closes #19178: backport entries for "module" and "package" from 3.x glossary. Patch by Berker Peksag.

Use the platform-independent way of calling a script from the shell: "python prog.py", not "prog.py"

Found by Micheal Wells on docs@.

Patch by Filip Gruszczyński.

Fix order of required StreamReader/StreamWriter base classes.  Spotted by Edward Welbourne on docs@.

Found by Helge Stenström on docs@.