Add a notice to the import screen about the import importing everything

This was first flagged by a user here:
https://www.reddit.com/r/EteSync/comments/hbdxf8/quickest_way_to_revert_an_import_into_address_book/

app/src/main/res/layout/fragment_local_calendar_import.xml

@@ -1,9 +1,22 @@
 <?xml version="1.0" encoding="utf-8"?>
-<ExpandableListView
-    xmlns:android="http://schemas.android.com/apk/res/android"
-    android:id="@android:id/list"
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
-    android:layout_height="wrap_content"
-    android:choiceMode="singleChoice"
-    android:descendantFocusability="beforeDescendants"/>
+    android:layout_height="match_parent"
+    android:orientation="vertical">
 
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:padding="8dp"
+        android:text="@string/import_account_top_notice"
+        android:textAppearance="?android:attr/textAppearanceMedium" />
+
+    <ExpandableListView
+        android:id="@android:id/list"
+        android:layout_width="match_parent"
+        android:layout_height="0dp"
+        android:layout_weight="1"
+        android:choiceMode="singleChoice"
+        android:descendantFocusability="beforeDescendants"/>
+
+</LinearLayout>

app/src/main/res/layout/fragment_local_contact_import.xml

@@ -1,8 +1,21 @@
 <?xml version="1.0" encoding="utf-8"?>
-<androidx.recyclerview.widget.RecyclerView
-    xmlns:android="http://schemas.android.com/apk/res/android"
-    android:id="@+id/recyclerView"
+<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
-    android:layout_height="wrap_content"
-    android:choiceMode="singleChoice"/>
+    android:layout_height="match_parent"
+    android:orientation="vertical">
 
+    <TextView
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
+        android:padding="8dp"
+        android:text="@string/import_account_top_notice"
+        android:textAppearance="?android:attr/textAppearanceMedium" />
+
+    <androidx.recyclerview.widget.RecyclerView
+        android:id="@+id/recyclerView"
+        android:layout_width="match_parent"
+        android:layout_height="0dp"
+        android:layout_weight="1"
+        android:choiceMode="singleChoice" />
+
+</LinearLayout>

app/src/main/res/values/strings.xml

@@ -251,6 +251,7 @@
     <string name="import_dialog_adding_entries">Adding entries...</string>
     <string name="import_dialog_success">Processed %1$d entries.\nAdded: %2$d\nChanged: %3$d\nSkipped (failed): %4$d</string>
     <string name="import_permission_required">Reading storage permission is required for import.</string>
+    <string name="import_account_top_notice">Please choose an account to import all of its entries from.</string>
     <string name="choose_file">Choose file</string>
 
     <!-- AccountSettingsActivity -->