Adds commented-out information on PA plugin

Author: aetter

docs/install/plugins.md

@@ -38,6 +38,23 @@ sudo bin/elasticsearch-plugin install https://d3g5vo6xdbdb9a.cloudfront.net/down
 ```
 
 
+{% comment %}
+#### Performance Analyzer
+
+```bash
+sudo bin/elasticsearch-plugin install https://d3g5vo6xdbdb9a.cloudfront.net/downloads/elasticsearch-plugins/performance-analyzer/opendistro_performance_analyzer-0.9.0.0.zip
+```
+
+Performance Analyzer requires so many additional configuration steps that we don't recommend installing it as a standalone plugin. After installing the plugin:
+
+1. Create `/usr/lib/systemd/system/opendistro-performance-analyzer.service` based on [this file](https://github.com/opendistro-for-elasticsearch/performance-analyzer/blob/master/packaging/opendistro-performance-analyzer.service).
+1. Create `/usr/share/elasticsearch/bin/performance-analyzer-agent-cli` based on [this file](https://github.com/opendistro-for-elasticsearch/performance-analyzer/blob/master/packaging/performance-analyzer-agent-cli).
+1. Run the `postinit` script for [RPM-based](https://github.com/opendistro-for-elasticsearch/performance-analyzer/tree/master/packaging/rpm) or [Debian-based](https://github.com/opendistro-for-elasticsearch/performance-analyzer/tree/master/packaging/deb) distributions.
+1. `sudo systemctl start elasticsearch.service`
+1. `curl -XGET "localhost:9600/_opendistro/_performanceanalyzer/metrics?metrics=Latency,CPU_Utilization&agg=avg,max&dim=ShardID&nodes=all"`
+{% endcomment %}
+
+
 ## Compatibility
 
 See [Version history](../../../#version-history) for the versions of Elasticsearch that Open Distro for Elasticsearch supports. You must have the exact compatible OSS version installed (e.g. 6.6.2 and not 6.6.1). To get a list of available Elasticsearch versions on CentOS 7 and Amazon Linux 2: