Adding Link To Installers in README

Hi Team,

There are pre-built installers of this plugin created for various operating systems as documented [here](https://docs.aws.amazon.com/systems-manager/latest/userguide/session-manager-working-with-install-plugin.html)

Please add this link in README file which can guide where to download installers from.

Other option would be to attach these installers as Release Artifact

Open the README and find the section that explains how to install or download the plugin. Add the linked AWS Systems Manager installer documentation, or confirm with maintainers whether the preferred outcome is attaching installers as release artifacts; the README should clearly guide users to the pre-built installers.

Written by the indexing model from the issue text.