docs: updates --routing-url to optional

CHANGELOG.md

@@ -32,6 +32,19 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
   [pull/487]: https://github.com/apollographql/rover/pull/487
 
 ## 🚀 Features
+
+- **`--routing-url` is now an optional argument to `rover subgraph publish` - [EverlastingBusgtopper], [issue/169] [pull/484]**
+
+  When publishing a subgraph, it is important to include a routing URL for that subgraph, so your graph router
+  knows where to route requests for types in a subgraph. Previously, you had to specify this argument on
+  every `rover subgraph publish`, but now it acts as an upsert, meaning you must include it on your first
+  `rover subgraph publish`, but subsequent publishes will retain the existing routing URL for a subgraph
+  if `--routing-url` is not specified.
+
+  [EverlastingBusgtopper]: https://github.com/EverlastingBusgtopper
+  [pull/484]: https://github.com/apollographql/rover/pull/484
+  [issue/169]: https://github.com/apollographql/rover/issues/169
+
 ## 🐛 Fixes
 ## 🛠 Maintenance
 

docs/source/subgraphs.md

@@ -180,9 +180,11 @@ Alternatively, you can provide `-`, in which case the command uses an SDL string
 
 <td>
 
-**Required.** Used by a gateway running in [managed federation mode](https://www.apollographql.com/docs/federation/managed-federation/overview/).
+The URL that your gateway uses to communicate with the subgraph in a [managed federation architecture](https://www.apollographql.com/docs/federation/managed-federation/overview/).
 
-If you're running a subgraph that hasn't been deployed yet or isn't using managed federation, you can pass a placeholder URL or leave the flag empty.
+**Required** the first time you publish a particular subgraph. Provide an empty string if your subgraph isn't deployed yet, or if you aren't using managed federation.
+
+**Optional** after your first publish. Provide only if you need to change the subgraph's routing URL.
 
 </td>
 </tr>