Add more info to README about default value of GITHUB_HOST env var

README.md

@@ -30,7 +30,7 @@ These containers are built via Github actions that [copy the dockerfile](https:/
 | `RUNNER_TOKEN` | If not using a PAT for `ACCESS_TOKEN` this will be the runner token provided by the Add Runner UI (a manual process). Note: This token is short lived and will change frequently. `ACCESS_TOKEN` is likely preferred. |
 | `RUNNER_WORKDIR` | The working directory for the runner. Runners on the same host should not share this directory. Default is '/_work'. This must match the source path for the bind-mounted volume at RUNNER_WORKDIR, in order for container actions to access files. |
 | `RUNNER_GROUP` | Name of the runner group to add this runner to (defaults to the default runner group) |
-| `GITHUB_HOST` | URL of the Github Enterprise server e.g github.mycompany.com |
+| `GITHUB_HOST` | Optional URL of the Github Enterprise server e.g github.mycompany.com. Defaults to `github.com`. |
 
 ## Examples ##