Mention New Feature in release notes

In conjunction with the FSCache feature, `git checkout`
[is now a lot faster when checking out a *lot* of
files](git-for-windows/git#1468).

Signed-off-by: Johannes Schindelin <[email protected]>

Author: dscho

ReleaseNotes.md

@@ -39,6 +39,7 @@ This package contains software from a number of other projects including Bash, z
 
 * When choosing to "Use Git from the Windows Command Prompt" (i.e. add only the minimal set of Git executables to the `PATH`), and when choosing the Git LFS component, Git LFS [is now included in that minimal set](https://github.com/git-for-windows/git/issues/1503).
 * Comes with [gawk v4.2.1](http://git.savannah.gnu.org/cgit/gawk.git/plain/NEWS?h=gawk-4.2.1).
+* In conjunction with the FSCache feature, `git checkout` [is now a lot faster when checking out a *lot* of files](https://github.com/git-for-windows/git/pull/1468).
 
 ### Bug Fixes