Currently, there is no eZ Find documentation for version 5.3.

There are some changes on the requirements, and Java Runtime Environment 7.x will be required as of eZ Find 5.3, in order to be able to start the Solr server.

This information should be available on doc.ez.no, as well as installation and configuration instructions.

The 5.2 docs can be used as a starting point to make the 5.3 doc:
https://doc.ez.no/Extensions/eZ-Publish-extensions/eZ-Find/eZ-Find-LS-5.2.0