ui: clarify TTS preload setting label

Author: JadenJSJ

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

@@ -162,7 +162,7 @@
                 android:layout_height="wrap_content"
                 android:minWidth="150dip"
                 android:singleLine="true"
-                android:text="Precompute sentences" />
+                android:text="TTS preload ahead" />
 
             <TextView
                 android:id="@+id/ttsPrecomputeLines"
@@ -279,4 +279,4 @@
             android:text="@string/speak_into_file_wav" />
     </LinearLayout>
 
-</ScrollView>
+</ScrollView>