Update supported Pythons list.

Fixes pyinstaller/pyinstaller/#5517.

Author: bwoodsend

features.rst

@@ -15,7 +15,8 @@ Features
   - Mac OS X (32-bit and 64-bit),
   - contributed suppport for FreeBSD, Solaris, HPUX, and AIX.
 
-* Multi-version: supports Python 2.7 and Python 3.5—3.7.
+* Multi-version: PyInstaller 4.2 supports Python 3.5—3.9.
+  Older versions of Python are usable with older versions of PyInstaller.
 
 * Flexible packaging mode:
 

index.rst

@@ -18,7 +18,7 @@
   help us a lot on solving the bug.
 
 PyInstaller's main advantages over similar tools are that
-PyInstaller works with Python 3.5—3.7, it builds smaller
+PyInstaller works with Python 3.5—3.9, it builds smaller
 executables thanks to transparent compression, it is fully
 multi-platform, and use the OS support to load the dynamic libraries,
 thus ensuring full compatibility.