Update SIEM-at-Home README.md

Update SIEM-at-Home README.md - Add note regarding blog 5

Author: rwaight

Security Analytics/SIEM-at-Home/README.md

@@ -4,7 +4,7 @@ Monitoring your servers and workstations doesn't have to be difficult or expensi
 2. [Securing cluster access](https://www.elastic.co/blog/elastic-siem-for-small-business-and-home-2-securing-cluster-access)
 3. [GeoIP data and Beats config review](https://www.elastic.co/blog/elastic-siem-for-small-business-and-home-3-geoip-data-and-beats-config-review)
 4. [Beats on Windows](https://www.elastic.co/blog/elastic-siem-for-small-business-and-home-4-beats-on-windows)
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+5. Beats on CentOS  _(coming soon)_
 
 ## `beats-configs`
 Example configurations for beats when deploying an Elastic SIEM at Home running on Elasticsearch Service