add DISCLAIMER to repo root (Apache Incubator)

[pjfanning]

This needs to appear in your source releases and binary artifacts but ideally should also be in your git repo because many users download the source using git.

https://incubator.apache.org/policy/incubation.html#disclaimers

Ideally this file should be exactly the same as the one that you put in your source release.
https://dist.apache.org/repos/dist/dev/incubator/ozhera/2.2.5-incubating-rc4/ apache-ozhera-2.2.5-incubating-src.tar.gz

[gaoxh]

The DISCLAIMER file of the source code has been synchronized and the current issue has been fixed. Thanks.