Add MaxConcurrentQueries documentation and update SECURITY.md to 1.6.x

Author: semihalev

README.md

@@ -178,6 +178,7 @@ example.com.		0	CH	HINFO	"Host" "IPv6:[2001:500:8d::53]:53 rtt:148ms health:[GOO
 | **roottcptimeout**   | TCP idle timeout for root server connections. Default: "5s"                                                          |
 | **tldtcptimeout**    | TCP idle timeout for TLD server connections (com, net, org, etc.). Default: "10s"                                   |
 | **tcpmaxconnections**| Maximum number of pooled TCP connections. 0 uses default. Default: 100                                               |
+| **maxconcurrentqueries** | Maximum number of concurrent DNS queries allowed. Limits resource usage under heavy load. Default: 10000         |
 | **dnstapsocket**     | Unix domain socket path for dnstap binary DNS logging. Leave empty to disable                                       |
 | **dnstapidentity**   | Server identity string for dnstap messages. Defaults to hostname                                                    |
 | **dnstapversion**    | Server version string for dnstap messages. Default: "sdns"                                                          |

SECURITY.md

@@ -6,8 +6,8 @@ Only the following version is currently being supported with security updates:
 
 | Version | Supported          |
 | ------- | ------------------ |
-| 1.3.x   | :white\_check\_mark: |
-| < 1.3   | :x:                |
+| 1.6.x   | :white\_check\_mark: |
+| < 1.6   | :x:                |
 
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