Add comment for night mode search keyword translations

Bug: 19562061
Change-Id: Ifb4100c721331379474d967d3f6ce7fd18a93ed4
diff --git a/res/values/strings.xml b/res/values/strings.xml
index 0e535c6..6923c14 100644
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -5542,6 +5542,7 @@
     <string name="keywords_display">screen touchscreen</string>
     <string name="keywords_display_brightness_level">dim screen touchscreen battery</string>
     <string name="keywords_display_auto_brightness">dim screen touchscreen battery</string>
+    <!-- Search keywords for display light/dark theme: dark theme, night mode, dim screen, invert brightness [CHAR LIMIT=NONE] -->
     <string name="keywords_display_night_mode">dark theme night mode dim screen invert brightness</string>
     <string name="keywords_display_wallpaper">background personalize customize display</string>
     <string name="keywords_display_font_size">text size</string>