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_003_nonstream.json b/updater_sample/tests/res/raw/update_config_003_nonstream.json
index 4175c35..7c78b9d 100644
--- a/updater_sample/tests/res/raw/update_config_003_nonstream.json
+++ b/updater_sample/tests/res/raw/update_config_003_nonstream.json
@@ -5,5 +5,5 @@
     },
     "ab_install_type": "NON_STREAMING",
     "name": "S ota_002_package",
-    "url": "file:///data/sample-ota-packages/ota_003_package.zip"
+    "url": "file:///data/my-sample-ota-builds-dir/ota_003_package.zip"
 }
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