ReleaseNotes: duplicated files are hard links

Inform users that Windows Explorer double counts file sizes for
hard links.

fixes: #1977 (git-for-windows/git#1997)

Signed-off-by: Philip Oakley <philipoakley@iee.org>

ReleaseNotes.md

@@ -23,6 +23,7 @@ See [http://git-scm.com/](http://git-scm.com/) for further details about Git inc
 *   Some commands are not yet supported on Windows and excluded from the installation.
 *   As Git for Windows is shipped without Python support, all Git commands requiring Python are not yet supported; e.g. `git p4`.
 *   The Quick Launch icon will only be installed for the user running setup (typically the Administrator). This is a technical restriction and will not change.
+*   The git-core executable file(s) are typically double-counted by Windows Explorer. In fact, repeated files are hard linked, so do not take up the space indicated (#1977).
 
 Should you encounter other problems, please search [the bug tracker](https://github.com/git-for-windows/git/issues) and [the mailing list](http://groups.google.com/group/git-for-windows), chances are that the problem was reported already. If it has not been reported, please follow [our bug reporting guidelines](https://github.com/git-for-windows/git/wiki/Issue-reporting-guidelines) and [report the bug](https://github.com/git-for-windows/git/issues/new).