remove extra /netdata on target directory to deploy plugin under Linux

Author: hugovalente-pm

README.md

@@ -113,7 +113,7 @@ This script will:
 
    ```
    unzip netdata-datasource-<version_number>.zip
-   cp -rf netdata-datasource/ /var/lib/grafana/plugins/netdata
+   cp -rf netdata-datasource/ /var/lib/grafana/plugins
    ```
 
 4. Ensure that Netdata plugin which currently isn’t signed can be registered