docs: Make Ubuntu install idempotent
Don't append to Kata-specific apt sources file to avoid apt warnings
and make the install idempotent.
Fixes
@@ -24,7 +24,7 @@ For more information on installing Docker please refer to the
**Note:** The repository is downloading content using `http`, be aware that this installation channel is not secure.
```bash
-$ sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/katacontainers:/release/xUbuntu_$(lsb_release -rs)/ /' >> /etc/apt/sources.list.d/kata-containers.list"
+$ sudo sh -c "echo 'deb http://download.opensuse.org/repositories/home:/katacontainers:/release/xUbuntu_$(lsb_release -rs)/ /' > /etc/apt/sources.list.d/kata-containers.list"
$ curl -sL http://download.opensuse.org/repositories/home:/katacontainers:/release/xUbuntu_$(lsb_release -rs)/Release.key | sudo apt-key add -
$ sudo -E apt-get update
$ sudo -E apt-get -y install kata-runtime kata-proxy kata-shim
