SipSettings: fix string and descriptions.

http://b/issue?id=3012773

Change-Id: I36484c17ef4b5711afe30e88067c675b65f954d3
diff --git a/res/values/strings.xml b/res/values/strings.xml
index af66cd7..60006e3 100755
--- a/res/values/strings.xml
+++ b/res/values/strings.xml
@@ -1282,7 +1282,7 @@
     <string name="primary_account_summary">Used for outbound calls.</string>
     <!-- Title of the advanced settings button. The button will show the advanced settings of a SIP account in the SIP editor [CHAR LIMIT=NONE] -->
     <string name="advanced_settings_title">Advanced settings</string>
-    <!-- Text of a primary account summary with registration status [CHAR LIMIT=NONE] -->
+    <!-- Summary of a SIP account in the list of SIP accounts, consists of primary account status and registration status. This string indicates that this SIP account is a primary account and the string placeholder is the registration status, which will be one of the strings with name starting with "registration_status_" below. [CHAR LIMIT=NONE] -->
     <string name="primary_account_summary_with">Primary account. %s</string>
     <!-- Text of Internet-call registration status, checking current registration status with SIP service [CHAR LIMIT=NONE] -->
     <string name="registration_status_checking_status">Checking status...</string>
@@ -1354,8 +1354,8 @@
     <!-- Hint to hide the advanced settings section. [CHAR LIMIT=NONE] -->
     <string name="advanced_settings_hide">▽ Select to hide all</string>
 
-    <!-- Showing that some preference field can not be empty in an alert dialog. [CHAR LIMIT=NONE] -->
-    <string name="empty_alert">%s cannot be empty.</string>
+    <!-- Text in an alert dialog telling the user that some input field is required and can not be left blank. [CHAR LIMIT=NONE] -->
+    <string name="empty_alert">%s is required, cannot be left blank.</string>
     <!-- Showing that port number is out of range in an alert dialog. [CHAR LIMIT=NONE] -->
     <string name="not_a_valid_port">Port number should be within 1000 and 65534.</string>