docs: Windows Security modifies Chromium checkout (#26151)

docs/development/build-instructions-windows.md

@@ -50,6 +50,13 @@ building with Visual Studio will come in the future.
 **Note:** Even though Visual Studio is not used for building, it's still
 **required** because we need the build toolchains it provides.
 
+## Exclude source tree from Windows Security
+
+Windows Security doesn't like one of the files in the Chromium source code
+(see https://crbug.com/441184), so it will constantly delete it, causing `gclient sync` issues.
+You can exclude the source tree from being monitored by Windows Security by
+[following these instructions](https://support.microsoft.com/en-us/windows/add-an-exclusion-to-windows-security-811816c0-4dfd-af4a-47e4-c301afe13b26).
+
 ## Building
 
 See [Build Instructions: GN](build-instructions-gn.md)