Mention New Feature in release notes

The FSCache feature [is now used with `git checkout` and `git reset`
in sparse checkouts](git-for-windows/git#2224).

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

ReleaseNotes.md

@@ -44,6 +44,7 @@ This package contains software from a number of other projects including Bash, z
 * Comes with [cURL v7.65.3](https://curl.haxx.se/changes.html#7_65_3).
 * Comes with [Git LFS v2.8.0](https://github.com/git-lfs/git-lfs/releases/tag/v2.8.0).
 * When configuring Git for Windows to use `plink`, [there is now a checkbox specifically for TortoisePlink](https://github.com/git-for-windows/build-extra/pull/251).
+* The FSCache feature [is now used with `git checkout` and `git reset` in sparse checkouts](https://github.com/git-for-windows/git/pull/2224).
 
 ### Bug Fixes