patch 8.2.3214: MS-Windows: passing /D does not set the install location

Problem:    MS-Windows: passing /D does not set the install location.
Solution:   Adjust how the installer uses $VIM. Update the documentation.
            (Christian Brabandt, closes #8605)
diff --git a/runtime/doc/os_win32.txt b/runtime/doc/os_win32.txt
index 3767cb8..1799faf 100644
--- a/runtime/doc/os_win32.txt
+++ b/runtime/doc/os_win32.txt
@@ -18,7 +18,8 @@
 4. Using the mouse		|win32-mouse|
 5. Running under Windows 95	|win32-win95|
 6. Running under Windows 3.1	|win32-win3.1|
-7. Win32 mini FAQ		|win32-faq|
+7. Installation package		|win32-installer|
+8. Win32 mini FAQ		|win32-faq|
 
 Additionally, there are a number of common Win32 and DOS items:
 File locations			|dos-locations|
@@ -175,7 +176,29 @@
 Support was removed in patch 7.4.1364.
 
 ==============================================================================
-7. Win32 mini FAQ					*win32-faq*
+7. Installation package					*win32-installer*
+
+A simple installer for windows is available at http://www.vim.org/download.php
+(stable version) and nightly builds are also available at
+https://github.com/vim/vim-win32-installer/releases/
+
+The nightly builds include 32bit and 64bit builds, have most features enabled
+and usually also contain an extra cryptographic signed installer, so Windows
+will not complain.
+
+To use the installer, simply run the exe file.  The following switches are
+also supported: >
+
+    gvim_<version>.exe /S           -> silent install without any dialogues
+    gvim_<version>.exe /D=C:\vim    -> Install into directory c:\vim
+                                    -> /D must be the last argument
+    gvim_<version>.exe /S /D=c:\vim -> silent install into c:\vim
+<
+The default installation directory can alternatively be given by setting the
+$VIM environment variable.
+
+==============================================================================
+8. Win32 mini FAQ					*win32-faq*
 
 Q. How do I change the font?
 A. In the GUI version, you can use the 'guifont' option.  Example: >