updater_sample: add privileged system app docs

README.md: add instructions

Test: on device
Bug: 80250430
Change-Id: I2e04fdefda2b73d01dfa0a8e684542feb2ed6c61
Signed-off-by: Zhomart Mukhamejanov <zhomart@google.com>
diff --git a/updater_sample/tests/res/raw/update_config_002_stream.json b/updater_sample/tests/res/raw/update_config_002_stream.json
index 5d7874c..40c8fe1 100644
--- a/updater_sample/tests/res/raw/update_config_002_stream.json
+++ b/updater_sample/tests/res/raw/update_config_002_stream.json
@@ -39,5 +39,5 @@
         ]
     },
     "name": "S ota_002_package",
-    "url": "file:///data/sample-ota-packages/ota_002_package.zip"
+    "url": "file:///data/my-sample-ota-builds-dir/ota_002_package.zip"
 }
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