Merge pull request #422 from joshpalis/plugins-doc

Modified plugin documentation by clarifying valid plugin ID inputs

_opensearch/install/plugins.md

@@ -21,9 +21,22 @@ You can install individual plugins on an OpenSearch cluster.
 
 ## Install a plugin
 
+The install command takes a plugin id, which may be any of the following:
+
+- An official OpenSearch plugin name
+- Maven coordinates to a plugin zip file
+- A URL to a plugin zip file
+
+If you're installing an official OpenSearch plugin, use:
 ```
 bin/opensearch-plugin install <plugin-name>
 ```
+
+For a plugin installed via zip, use:
+```
+bin/opensearch-plugin install <name|Zip File|Url>
+```
+
 Restart your OpenSearch node after installing a plugin.
 
 ## Remove a plugin