updated README and installation docu (#465)

var/docs/updates.md

@@ -0,0 +1,36 @@
+# Updating Kimai
+
+> **NOTE**
+> 
+> Don't forget that some tweaks may be necessary to these instructions if you are using FTP, developing or updating on your 
+personal computer instead of a server. Read the [installation docu](installation.md) for more information.
+
+**STOP** 
+
+1. It is important that you don't execute the installation steps before or after your update
+2. Make sure that you have a working database backup before you start the update
+3. Read the [UPGRADING](https://github.com/kevinpapst/kimai2/blob/master/UPGRADING.md) guide and the [release information](https://github.com/kevinpapst/kimai2/releases) to check if there are further steps required
+
+**START** 
+
+Change into your Kimai 2 installation directory, then fetch the latest code and install all dependencies:
+
+```bash
+git pull origin master
+sudo -u www-data composer install --no-dev --optimize-autoloader
+```
+
+Refresh your cache:
+
+```bash
+sudo -u www-data bin/console cache:clear --env=prod
+sudo -u www-data bin/console cache:warmup --env=prod
+```
+
+And upgrade your database:
+
+```bash
+bin/console doctrine:migrations:migrate
+```
+
+Done! You can use the latest version of Kimai 2.