help: Document new setting for moving a topic between streams.

I'd like to do more refactoring on this documentation, but at least we
now explain the current model accurately.

templates/zerver/help/community-topic-edits.md

@@ -28,3 +28,4 @@ for details.
 ## Related articles
 
 * [Message and topic editing](/help/configure-message-editing-and-deletion)
+* [Rename a topic](/help/rename-a-topic)

templates/zerver/help/configure-message-editing-and-deletion.md

@@ -21,6 +21,7 @@ is highly configurable. Two things are true under any configuration:
 | Edit your message topics           | [1]      | [1]     |
 | Add a topic to a topicless message | [1]      | [1]     |
 | Edit others' message topics        | [1]      | [2]     |
+| Move topics between streams        | [4]      | [4]     |
 | Delete your messages               | ✔ | [3]     |
 | Delete others' messages            | ✔ |         |
 
@@ -30,6 +31,9 @@ is highly configurable. Two things are true under any configuration:
 
 [3] Controlled by **Allow message deleting**.
 
+[4] Controlled by **Who can move messages between streams**, in
+addition to other restrictions on editing topics.
+
 There are a few useful things to understand about the message editing
 settings.
 
@@ -60,7 +64,24 @@ You can access the message editing and deletion settings as follows.
 
 {end_tabs}
 
+### Configure who can move topics between streams
+
+By default, only organization administrators can move topics between
+streams.  You can configure which roles have permission to do so:
+
+{start_tabs}
+
+{settings_tab|organization-permissions}
+
+2. Under **Stream permissions**, configure **Who can move messages between streams**.
+
+{!save-changes.md!}
+
+{end_tabs}
+
 ## Related articles
 
 * [Disable message edit history](/help/disable-message-edit-history)
 * [Configure message retention policy](/help/message-retention-policy)
+* [Rename a topic](/help/rename-a-topic)
+* [Community topic edits](/help/community-topic-edits)

templates/zerver/help/rename-a-topic.md

@@ -34,10 +34,11 @@ for the details on when topic editing is allowed.
 
 ## Move a topic to another stream
 
-{!admin-only.md!}
+Organizations can configure which roles have permission to [move
+topics between streams][move-permission-setting].
 
-Organization administrators can move a topic from one stream to
-another.
+To move a topic, you must have access to both the source and
+destination streams.
 
 {start_tabs}
 
@@ -64,9 +65,10 @@ another.
 
 ## Move message(s) in a topic to another stream
 
-{!admin-only.md!}
+Organizations can configure which roles have permission to [move
+topics between streams][move-permission-setting].
 
-Organization administrators can also move only a subset of messages
+Roles that have permission can also move only a subset of messages
 from a topic to another stream.
 
 {start_tabs}
@@ -95,5 +97,6 @@ option.
 !!! warn ""
     **Note**: You cannot edit content of a message while changing its stream.
 
-
 {end_tabs}
+
+[move-permission-setting]: /help/configure-message-editing-and-deletion#configure-who-can-move-topics-between-streams