Updated README file

Author: Jakub Krkoska

README.md

@@ -1,2 +1,18 @@
 # mysql-backup
 Backups mysql database using mysql dump.
+
+## Crontab
+- backups are being done by crontab, which runs backup.sh script in set interval
+- with each backup the size and duration of the backup are being logged
+    - these logs are optionally saved to the database as well
+    - log database shoud be named 'logs'
+        - there should be one table named 'backup_logs' with 3 columns(duration, backup_size, backup_name)
+
+## Env variables
+DB_HOST -> database host, either domain name or IP address
+DB_PORT -> database port
+DB_USERNAME -> database username
+DB_PASSWORD -> database password
+DB_NAME -> name of the database which should be backed up
+CRON_SCHEDULE_PATTERN -> pattern for cron which specifies how often should be the backups done (default value set to '0 */2 * * *')
+WRITE_LOGS -> whether to write logs to log database (default value set to 0)