Add string for Installing_security_update

Bug: 27837319
Change-Id: I037158697a294c3e03f186f3b4207ea700321a8a
(cherry picked from commit 1ee0ff3d78c5143d4e3307bc44e3c27792e72d1e)
diff --git a/tools/recovery_l10n/res/values/strings.xml b/tools/recovery_l10n/res/values/strings.xml
index 3a8aeec..f6193ab 100644
--- a/tools/recovery_l10n/res/values/strings.xml
+++ b/tools/recovery_l10n/res/values/strings.xml
@@ -31,4 +31,8 @@
        LIMIT=60] -->
   <string name="recovery_error">Error!</string>
 
+  <!-- Displayed on the screen beneath the animation while the
+       system is installing a security update. [CHAR LIMIT=60] -->
+  <string name="recovery_installing_security">Installing security update\u2026</string>
+
 </resources>