Add section of tools for realtime indexing

[LifeIsStrange]

such as:

• Hibernate Search
• zombodb
• https://github.com/scharron/elasticsearch-river-mysql
• Kafka ?

special mention for Lucene NRT

Realtime indexing allow for search results to be in sync with the current state of the database, which is a majorly useful feature.
If I understand correctly, most people use periodic (non-realtime) full patch with tools such as logstash to reindex ELK. I wonder what the industry actually use for this need since the river drivers are unmaintained and hibernate search and zombodb are not well known.