Fix #38 use gren to create release notes

.grenrc

@@ -0,0 +1,5 @@
+{
+    "onlyMilestones": false,
+    "groupBy": "label",
+    "changelogFilename": "CHANGELOG.md"
+}

README.md

@@ -11,9 +11,10 @@ Après avoir cloné, veuillez positionner les hooks git:
 ./git/hooks/setup.sh
 ```
 
-### Robot activés
+### Services ou robots activés
 
 | badge  | nom   | description  |
 |--------|-------|:--------|
 | [![Build Status](https://travis-ci.com/boly38/jardiCal.svg?branch=master)](https://travis-ci.com/boly38/jardiCal) |[Travis-ci](https://travis-ci.com/github/boly38/jardiCal)|Tests continus.
 |  |[Houndci](https://houndci.com/)|Relecture de code JavaScript (configuré via `.hound.yml`, voir aussi [eslint](.eslint.md))|
+| [![Automated Release Notes by gren](https://img.shields.io/badge/%F0%9F%A4%96-release%20notes-00B2EE.svg)](https://github-tools.github.io/github-release-notes/)|[gren](https://github.com/github-tools/github-release-notes)|Création automatisée de [release notes](https://github.com/boly38/jardiCal/releases)|