Update various OS X README files for 3.3.0.
diff --git a/Mac/BuildScript/resources/ReadMe.txt b/Mac/BuildScript/resources/ReadMe.txt
index f1beda0..9ac52d0 100644
--- a/Mac/BuildScript/resources/ReadMe.txt
+++ b/Mac/BuildScript/resources/ReadMe.txt
@@ -5,8 +5,15 @@
 Installation requires approximately $INSTALL_SIZE MB of disk space,
 ignore the message that it will take zero bytes.
 
-You must install onto your current boot disk, even though the
-installer does not enforce this, otherwise things will not work.
+If you are attempting to install on an OS X 10.8 system, you may
+see a message that Python can't be installed because it is from an
+unidentified developer.  This is because this Python installer
+package is not yet compatible with the Gatekeeper security feature
+introduced in OS X 10.8.  To allow Python to be installed, you
+can override the Gatekeeper policy for this install.  In the Finder,
+instead of double-clicking, control-click or right click the "Python"
+installer package icon.  Then select "Open using ... Installer" from
+the contextual menu that appears.
 
 Python consists of the Python programming language interpreter, plus
 a set of programs to allow easy access to it for Mac users including
@@ -16,10 +23,11 @@
 
                     **** IMPORTANT ****
                     
-Before using IDLE or other programs using the tkinter graphical user
-interface toolkit, visit http://www.python.org/download/mac/tcltk/
-for current information about supported and recommended versions
-of Tcl/Tk for this version of Python and Mac OS X.
+To use IDLE or other programs that use the tkinter graphical user
+interface toolkit, you may need to install a third-party version of
+the Tcl/Tk frameworks.  Visit http://www.python.org/download/mac/tcltk/
+for current information about supported and recommended versions of
+Tcl/Tk for this version of Python and of Mac OS X.
 
                     *******************
 
@@ -32,5 +40,13 @@
 well. Double-click on the "Update Shell Profile" command to add the
 "bin" directory inside the framework to your shell's search path.
 
+You must install onto your current boot disk, even though the
+installer does not enforce this, otherwise things will not work.
+
+You can verify the integrity of the disk image file containing the
+installer package and this ReadMe file by comparing its md5 checksum
+and size with the values published on the release page linked at
+http://www.python.org/download/
+
 More information on Python in general can be found at
 http://www.python.org.