Update README.md fix path typo (opensearch-project#253)

Missing /usr/share/logstash/ in the last command

Signed-off-by: Yohann Fabri <11197007+YoranSys@users.noreply.github.com>

Author: YoranSys

README.md

@@ -110,7 +110,7 @@ Starting in 2.0.0, the aws sdk version is bumped to v3. In order for all other A
 /usr/share/logstash/bin/logstash-plugin remove logstash-output-cloudwatch
 
 /usr/share/logstash/bin/logstash-plugin install --version 0.1.0.pre logstash-integration-aws
-bin/logstash-plugin install --version 2.0.0 logstash-output-opensearch
+/usr/share/logstash/bin/logstash-plugin install --version 2.0.0 logstash-output-opensearch
 ```
 ## ECS Compatibility
 [Elastic Common Schema(ECS)](https://www.elastic.co/guide/en/ecs/current/index.html]) compatibility for V8 was added in 1.3.0. For more details on ECS support refer to this [documentation](docs/ecs_compatibility.md).