Fix self-referencing links in Brand Guides README

The file was copied from overview.md but renamed to README.md, so
internal anchor links need to reference README.md instead.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: louis-pre

docs/brand-guides/README.md

@@ -11,10 +11,10 @@ Seam enables you to control a wide variety of devices and systems, from differen
 
 To find the integration guide for each of your devices or systems, see the following categories:
 
-* [Smart locks](overview.md#smart-locks)
-* [Access control systems](overview.md#access-control-systems)
-* [Thermostats](overview.md#thermostats)
-* [Noise sensors](overview.md#noise-sensors)
+* [Smart locks](README.md#smart-locks)
+* [Access control systems](README.md#access-control-systems)
+* [Thermostats](README.md#thermostats)
+* [Noise sensors](README.md#noise-sensors)
 
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