Wrong key "hostname" in documentation

[raiblue]

Given example in README.md, mysql source section:

mysql_data_source: &pii
  hostname: localhost

But there is no "hostname" key there actually, it must be "host". When hostname is used it has no effect and default value for host key is taken (localhost and unix socket usage).

You can fix the example as:

mysql_data_source: &pii
  host: localhost

[prezmix]

Thank you!