Update macOS installer display files for 3.9.0a1 (GH-16765)

diff --git a/Mac/BuildScript/resources/Welcome.rtf b/Mac/BuildScript/resources/Welcome.rtf
index 053084d..bf6aebe 100644
--- a/Mac/BuildScript/resources/Welcome.rtf
+++ b/Mac/BuildScript/resources/Welcome.rtf
@@ -1,4 +1,4 @@
-{\rtf1\ansi\ansicpg1252\cocoartf1671\cocoasubrtf500
+{\rtf1\ansi\ansicpg1252\cocoartf1671\cocoasubrtf600
 \cocoascreenfonts1{\fonttbl\f0\fswiss\fcharset0 Helvetica;\f1\fswiss\fcharset0 Helvetica-Bold;\f2\fmodern\fcharset0 CourierNewPSMT;
 }
 {\colortbl;\red255\green255\blue255;}
@@ -14,15 +14,17 @@
 \
 
 \f1\b Python for macOS
-\f0\b0  consists of the Python programming language interpreter, plus a set of programs to allow easy access to it for macOS users including an integrated development environment 
+\f0\b0  consists of the {\field{\*\fldinst{HYPERLINK "https://www.python.org"}}{\fldrslt Python}} programming language interpreter and its batteries-included standard library to allow easy access to macOS features.  It also includes the Python integrated development environment, 
 \f1\b IDLE
-\f0\b0 .\
+\f0\b0 .  You can also use the included 
+\f1\b pip
+\f0\b0  to download and install third-party packages from the {\field{\*\fldinst{HYPERLINK "https://pypi.org"}}{\fldrslt Python Package Index}}. \
 \
 At the end of this install, click on 
 \f2 Install Certificates
-\f0  for SSL root certificates\
+\f0  to install a set of current SSL root certificates.\
 \
 
 \f1\b NOTE: 
-\f0\b0 This is a beta test preview of Python 3.8.0, the next feature release of Python 3.8.  It is not intended for production use.\
+\f0\b0 This is an alpha test preview of Python 3.9.0, the next feature release of Python 3.  It is not intended for production use.\
 }
\ No newline at end of file