Add EC connectivity reqs (#2576)

Author: ajp-io

docs/partials/embedded-cluster/_requirements.mdx

@@ -7,4 +7,5 @@
   * The filesystem at `/var/lib/k0s` has 40Gi or more of total space and must be no more than 80% full
   * The filesystem at `/var/openebs` has 5Gi or more of total space
   * The filesystem at `/tmp` has 5Gi or more of total space
+* (Online installations only) Access to replicated.app and proxy.replicated.com or your custom domain for each
 * Embedded Cluster is based on k0s, so all k0s system requirements apply. See [System requirements](https://docs.k0sproject.io/stable/system-requirements/) in the k0s documentation.