Improve documentation for C:\ProgramData\Git\config

Move the description for the additional Git for Windows configuration file
into the right place, so that the following descriptions of the read priority
also covers this file correctly.

Also make it clear, what file `git config --system` selects.

Signed-off-by: Andreas Heiduk <[email protected]>

Author: asheiduk

Documentation/git-config.txt

@@ -235,8 +235,16 @@ FILES
 If not set explicitly with `--file`, there are four files where
 'git config' will search for configuration options:
 
+$PROGRAMDATA/Git/config::
+	(Windows-only) System-wide configuration file shared with other Git
+	implementations. Typically `$PROGRAMDATA` points to `C:\ProgramData`.
+
 $(prefix)/etc/gitconfig::
 	System-wide configuration file.
+	(Windows-only) This file contains only the settings which are
+	specific for this installation of Git for Windows and which should
+	not be shared with other Git implementations like JGit, libgit2.
+	`--system` will select this file.
 
 $XDG_CONFIG_HOME/git/config::
 	Second user-specific configuration file. If $XDG_CONFIG_HOME is not set
@@ -253,13 +261,6 @@ $XDG_CONFIG_HOME/git/config::
 $GIT_DIR/config::
 	Repository specific configuration file.
 
-On Windows, as there is no central `/etc/` directory, there is yet another
-config file (located at `$PROGRAMDATA/Git/config`), intended to contain
-settings for *all* Git-related software running on the machine. Consequently,
-this config file takes an even lower precedence than the
-`$(prefix)/etc/gitconfig` file. Typically `$PROGRAMDATA` points to
-`C:\ProgramData`.
-
 If no further options are given, all reading options will read all of these
 files that are available. If the global or the system-wide configuration
 file are not available they will be ignored. If the repository configuration