[readme]: update note regarding GH CLI and SSH requirement for custom images

Author: legomushroom

README.md

@@ -34,7 +34,7 @@ sudo gh extension install github/gh-net
 
 The `sudo` is required during extension installation on Linux due to https://github.com/cli/cli/issues/5456. Hopefully it won't be the case in the future.
 
-⚠️ If your Codespaces use non-default image, make sure that [GitHub CLI](https://cli.github.com/) is installed inside the Codespaces. The installation step can happen either in `Dockerfile` or in one of the `.devcontainer.json` lifecycle hooks e.g. [postCreateCommand](https://code.visualstudio.com/docs/remote/devcontainerjson-reference). See https://github.com/cli/cli#installation for GitHub CLI installation instructions.
+⚠️ If your Codespaces use non-default image, make sure that [GitHub CLI](https://cli.github.com/) and SSH server are installed inside the Codespaces. It might be as simple as adding `"github-cli": "latest"` and `"sshd": "latest"` to `devcontainer.json` file!
 
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