Provide a separate post-install README for MSI.

The old README.txt instructed you to manually update PATH if you
wanted to run pscp from a command prompt. But the MSI installer can do
that automatically, so the wording needs tweaks. And now that we're
actually launching README (at least optionally) from the installer UI,
it's more important to not make it look silly.

windows/README-msi.txt

@@ -0,0 +1,45 @@
+PuTTY README
+============
+
+This is the README file for the PuTTY MSI installer distribution. If
+you're reading this, you've probably just run our installer and
+installed PuTTY on your system.
+
+What should I do next?
+----------------------
+
+If you want to use PuTTY to connect to other computers, or use PSFTP
+to transfer files, you should just be able to run them from the
+Start menu.
+
+If you want to use the command-line file transfer utility PSCP, you
+will need to run this from a Command Prompt or equivalent, because it
+will not do anything useful without command-line options telling it
+what files to copy to and from where. You can do this by just running
+the command 'pscp' from a Command Prompt, if you used the installer's
+option to put the PuTTY installation directory on your PATH.
+Alternatively, you can always run pscp.exe by its full pathname, e.g.
+"C:\Program Files\PuTTY\pscp.exe".
+
+(Note that a Command Prompt that was already open before you ran the
+installer will not have inherited the update of PATH.)
+
+Some versions of Windows will refuse to run HTML Help files (.CHM)
+if they are installed on a network drive. If you have installed
+PuTTY on a network drive, you might want to check that the help file
+works properly. If not, see http://support.microsoft.com/kb/896054
+for information on how to solve this problem.
+
+What do I do if it doesn't work?
+--------------------------------
+
+The PuTTY home web site is
+
+    http://www.chiark.greenend.org.uk/~sgtatham/putty/
+
+Here you will find our list of known bugs and pending feature
+requests. If your problem is not listed in there, or in the FAQ, or
+in the manuals, read the Feedback page to find out how to report
+bugs to us. PLEASE read the Feedback page carefully: it is there to
+save you time as well as us. Do not send us one-line bug reports
+telling us `it doesn't work'.

windows/installer.wxs

@@ -162,7 +162,7 @@
           <Component Id="README_Component"
                      Guid="0AB63F2A-0FD9-4961-B8F7-AB85C22D9986">
             <File Id="README_File"
-                  Source="README.txt" KeyPath="yes" />
+                  Source="README-msi.txt" Name="README.txt" KeyPath="yes" />
           </Component>
 
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