docs: update thread edit docs (#2034)

Signed-off-by: plun1331 <49261529+plun1331@users.noreply.github.com>
Signed-off-by: Lala Sabathil <aiko@aitsys.dev>
Co-authored-by: Lala Sabathil <lala@pycord.dev>

discord/threads.py

@@ -611,7 +611,7 @@ async def edit(
         Editing the thread requires :attr:`.Permissions.manage_threads`. The thread
         creator can also edit ``name``, ``archived`` or ``auto_archive_duration``.
         Note that if the thread is locked then only those with :attr:`.Permissions.manage_threads`
-        can unarchive a thread.
+        can send messages in it or unarchive a thread.
 
         The thread must be unarchived to be edited.