Updated the docs to include new agent information

As we added the new column to the agents' list
that shows the agent's version,
we need to update the corresponding docs.

Changelog: changed

doc/user/clusters/agent/install/index.md

@@ -158,6 +158,7 @@ information to the cluster automatically without downtime.
 
 ## View your Agents
 
+> The version of installed `agentk` shown on the Agent tab [introduced](https://gitlab.com/gitlab-org/gitlab/-/issues/340882) in GitLab 14.8.
 If you have at least the Developer role, you can access the Agent's
 configuration repository and view the Agent's list:
 
@@ -168,6 +169,7 @@ On this page, you can view:
 
 - All the registered Agents for the current project.
 - The connection status.
+- The version of `agentk` installed on your cluster.
 - The path to each Agent's configuration file.
 
 Furthermore, if you select one of the Agents on your list, you can view its