Update README to mention Windows and/or Docker support

Author: mpdude

README.md

@@ -6,6 +6,8 @@ This action
 * loads a private SSH key into the agent and
 * configures `known_hosts` for GitHub.com.
 
+It should work in all GitHub Actions virtual environments, including container-based workflows. Windows and Docker support is, however, somewhat new. Since we have little feedback from the field, things might not run so smooth for you as we'd hope. If Windows and/or Docker-based workflows work well for you, leave a :+1: at #17.
+
 ## Why?
 
 When running a GitHub Action workflow to stage your project, run tests or build images, you might need to fetch additional libraries or _vendors_ from private repositories.
@@ -68,10 +70,6 @@ The `$SSH_AGENT_PID` contains the process id of the agent. This is used to kill
 
 ## Known issues and limitations
 
-### Currently OS X and Linux only
-
-This action has not been tested for the Windows virtual environment. If you can provide the steps necessary to setup (even install?) OpenSSH on the Windows machine, please open an issue. 
-
 ### Works for the current job only
 
 Since each job [runs in a fresh instance](https://help.github.com/en/articles/about-github-actions#job) of the virtual environment, the SSH key will only be available in the job where this action has been referenced. You can, of course, add the action in multiple jobs or even workflows. All instances can use the same `SSH_PRIVATE_KEY` secret.