add include and includeAll section to readme
add include and includeAll section to readme

It is unclear and takes me some time to get that path must be started with `conf/liquibase` part. 

I tried lots of other variants as: `liquibase/schema`, `classpath:liquibase/schema`, `classpath:liquibase/schema/`, `schema` with different types of relativeToChangelogFile flag and so on.

Documentation improvement is here.
Ticketfly/play-liquibase