sipcapture: updated README to document exported variables

- Added an "Exported pseudo-variabled" to the README file to document
  $hep(src_ip) and $hep(dst_ip)

src/modules/sipcapture/README

@@ -55,12 +55,17 @@ Alexandr Dubovikov
               4.1. sip_capture([table])
               4.2. report_capture([table],[data])
 
-        5. RPC Commands
+        5. Exported pseudo-variables
 
-              5.1. sipcapture.status param
+              5.1. $hep(src_ip)
+              5.2. $hep(dst_ip)
 
-        6. Database setup
-        7. Limitations
+        6. RPC Commands
+
+              6.1. sipcapture.status param
+
+        7. Database setup
+        8. Limitations
 
    List of Examples
 
@@ -125,12 +130,16 @@ Chapter 1. Admin Guide
         4.1. sip_capture([table])
         4.2. report_capture([table],[data])
 
-   5. RPC Commands
+   5. Exported pseudo-variables
+        5.1. $hep(src_ip)
+        5.2. $hep(dst_ip)
+
+   6. RPC Commands
 
-        5.1. sipcapture.status param
+        6.1. sipcapture.status param
 
-   6. Database setup
-   7. Limitations
+   7. Database setup
+   8. Limitations
 
 1. Overview
 
@@ -505,11 +514,26 @@ report_capture("report_data");
 report_capture("report_data", "{\"MOS\":4.1,\"PACKET_LOST\":100"});
 ...
 
-5. RPC Commands
+5. Exported pseudo-variables
+
+   5.1. $hep(src_ip)
+   5.2. $hep(dst_ip)
+
+   Exported pseudo-variables are listed in the next sections.
+
+5.1. $hep(src_ip)
+
+   Returns the current HEP's message original source IP address.
+
+5.2. $hep(dst_ip)
+
+   Returns the current HEP's message original destination IP address.
+
+6. RPC Commands
 
-   5.1. sipcapture.status param
+   6.1. sipcapture.status param
 
-5.1.  sipcapture.status param
+6.1.  sipcapture.status param
 
    Name: sipcapture.status
 
@@ -527,7 +551,7 @@ kamcmd sipcapture.status off
 kamcmd sipcapture.status check
 ...
 
-6. Database setup
+7. Database setup
 
    Before running Kamailio with the sipcapture module, you have to setup
    the database tables where the module will store the data. For that, if
@@ -537,7 +561,7 @@ kamcmd sipcapture.status check
    find the complete database documentation on the project webpage,
    http://www.kamailio.org/docs/db-tables/kamailio-db-devel.html.
 
-7. Limitations
+8. Limitations
 
      * 1. Only one capturing mode on RAW socket is supported: IPIP or
        monitoring/mirroring port. Don't activate both at the same time.