closes bpo-35630: Use code tag for 'python3' in 'README.rst' (GH-11394)

README.rst

@@ -63,7 +63,7 @@ On Unix, Linux, BSD, macOS, and Cygwin::
     make test
     sudo make install
 
-This will install Python as python3.
+This will install Python as ``python3``.
 
 You can pass many options to the configure script; run ``./configure --help``
 to find out more.  On macOS and Cygwin, the executable is called ``python.exe``;