prepare release 0.3 (#231)

UPGRADING.md

@@ -0,0 +1,21 @@
+# Upgrading Kimai 2
+
+## [0.3](https://github.com/kevinpapst/kimai2/releases/tag/0.3) (2018-07-22)
+
+**Update from 0.2:**
+
+You need to adjust your `.env` file and add your `from` address for [all emails](https://github.com/kevinpapst/kimai2/blob/master/var/docs/emails.md) generated by Kimai 2:
+```
+MAILER_FROM=kimai@example.com
+```
+
+Create a file and database backup before executing the following steps: 
+
+```bash
+git pull origin master
+sudo -u www-data composer install --no-dev --optimize-autoloader
+sudo -u www-data bin/console cache:clear --env=prod
+sudo -u www-data bin/console cache:warmup --env=prod
+bin/console doctrine:migrations:version --add 20180701120000
+bin/console doctrine:migrations:migrate
+```