android: name all four permissions WorkManager adds, not one

The note added with the previous commit said RECEIVE_BOOT_COMPLETED arrives in
the merged manifest via WorkManager. True, and incomplete — it brings four:
RECEIVE_BOOT_COMPLETED, ACCESS_NETWORK_STATE, WAKE_LOCK and FOREGROUND_SERVICE.

A comment whose whole job is "here is why the permission list has entries this
file does not declare" fails at that job if it accounts for one of them. Each
now says what it is for, checked against the built APK's merged manifest rather
than the library's — which is the version a person actually sees.

android/app/src/main/AndroidManifest.xml

@@ -9,11 +9,22 @@
     <uses-permission android:name="android.permission.INTERNET" />
 
     <!--
-      RECEIVE_BOOT_COMPLETED is NOT declared here and still ends up in the merged
-      manifest: WorkManager contributes it, so the periodic sync survives a
-      restart instead of silently stopping until the app is next opened. Noted
-      because it shows in the app's permission list and there is otherwise
-      nothing in this file to explain where it came from.
+      Four more permissions are NOT declared here and still reach the merged
+      manifest, contributed by WorkManager for the automatic sync:
+
+        RECEIVE_BOOT_COMPLETED  reschedules the periodic sync after a restart,
+                                instead of it silently stopping until the app is
+                                next opened by hand
+        ACCESS_NETWORK_STATE    evaluates the "needs a network" constraint, so a
+                                run is not attempted with no route to the server
+        WAKE_LOCK               holds the device awake for the seconds a sync
+                                takes, so it is not suspended mid-request
+        FOREGROUND_SERVICE      used only for expedited work; nothing here asks
+                                for it, and it arrives with the library
+
+      Verified against the built APK's merged manifest, not assumed. Noted here
+      because all four appear in the app's permission list and nothing else in
+      this file would explain where they came from.
     -->
 
     <!--