Issue #16115: Merge subprocess.Popen() documentation improvements from 3.3.

diff --cc Misc/NEWS
index ff6abb145596c8cec1cff367a2bac72756641a7a,184932fd4cadbd71a7d6e97fba64fd6d60b3c900..a5b57b85d1d3b85e12dd83c18b76bfe63fe3ae13
--- 1/Misc/NEWS
--- 2/Misc/NEWS
+++ b/Misc/NEWS
@@@ -155,9 -124,9 +155,12 @@@ Buil
  Documentation
  -------------
  
+ - Issue #16115: Improve subprocess.Popen() documentation around args, shell,
+   and executable arguments.
+ 
 +- Issue #13498: Clarify docs of os.makedirs()'s exist_ok argument.  Done with
 +  great native-speaker help from R. David Murray.
 +
  - Issue #15533: Clarify docs and add tests for `subprocess.Popen()`'s cwd
    argument.