added warning for ES 7.5 being incompatible (#114)
added warning for ES 7.5 being incompatible (#114)

* added warning for ES 7.5 being incompatible

See issue https://github.com/zammad/zammad/issues/2824

Currently we only support ES up to 7.4.X

* Update install-elasticsearch.rst

Text review.

zammad/zammad-documentation,zammad/zammad-documentation