added disclaimer about network segments due to Serf limitations (#7004)

* added disclaimer about network segments due to Serf limitations

using work made at https://github.com/hashicorp/consul/pull/6558 by @thepomeranian

* Lowercasing functionality name

* Update website/source/docs/enterprise/network-segments/index.html.md

Co-Authored-By: kaitlincarter-hc <43049322+kaitlincarter-hc@users.noreply.github.com>

Co-authored-by: kaitlincarter-hc <43049322+kaitlincarter-hc@users.noreply.github.com>

website/source/docs/enterprise/network-segments/index.html.md

@@ -18,6 +18,8 @@ with each other.
 To get started with Network Segments,
 [read the guide](https://learn.hashicorp.com/consul/day-2-operations/network-segments).
 
+~> **Note:** Due to limitations in [Serf](https://www.consul.io/docs/internals/gossip.html), a Consul agent configured with too many network segments may not be able to start
+
 # Consul Networking Models
 
 To help set context for this feature, it is useful to understand the various