Mention New Feature in release notes

The Git Bash prompt [can now be overridden by creating the file
`.config\git\git-prompt.sh`](#145).

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

Author: dscho

ReleaseNotes.md

@@ -38,6 +38,7 @@ This package contains software from a number of other projects including Bash, z
 ### New Features
 
 * Upgraded Git Credential Manager to [version 1.10.1](https://github.com/Microsoft/Git-Credential-Manager-for-Windows/releases/tag/v1.10.1).
+* The Git Bash prompt [can now be overridden by creating the file `.config\git\git-prompt.sh`](https://github.com/git-for-windows/build-extra/pull/145).
 
 ## Changes since Git for Windows v2.13.1 (June 13th 2017)