Update copy for PIN setting.

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

@@ -1873,7 +1873,7 @@
     <string name="preferences_app_protection__pin">PIN</string>
     <string name="preferences_app_protection__change">Change</string>
     <string name="preferences_app_protection__create">Create</string>
-    <string name="preferences_app_protection__your_pin_adds_an_extra_layer_of_security_and_backs">Your PIN adds an extra layer of security and backs up your account. You\'ll be asked for it when you register your phone number with Signal. If you forget your PIN, you\'ll be locked out of your account for 7 days.</string>
+    <string name="preferences_app_protection__your_pin_adds_an_extra_layer_of_security_to_your_account">Your PIN adds an extra layer of security to your account. You\'ll be asked for it when you register your phone number with Signal. If you forget your PIN, you\'ll be locked out of your account for 7 days.</string>
     <string name="AppProtectionPreferenceFragment_none">None</string>
     <string name="registration_activity__the_registration_lock_pin_is_not_the_same_as_the_sms_verification_code_you_just_received_please_enter_the_pin_you_previously_configured_in_the_application">The Registration Lock PIN is not the same as the SMS verification code you just received. Please enter the PIN you previously configured in the application.</string>
     <string name="registration_activity__registration_lock_pin">Registration Lock PIN</string>

app/src/main/res/xml/preferences_app_protection.xml

@@ -115,7 +115,7 @@
             android:widgetLayout="@layout/kbs_pin_change_preference"
             android:key="pref_kbs_change"
             android:title="@string/preferences_app_protection__pin"
-            android:summary="@string/preferences_app_protection__your_pin_adds_an_extra_layer_of_security_and_backs" />
+            android:summary="@string/preferences_app_protection__your_pin_adds_an_extra_layer_of_security_to_your_account" />
     </PreferenceCategory>
 
 </PreferenceScreen>