Update README.md

Author: svc-developer

README.md

@@ -39,7 +39,8 @@ const config = {
     logLevel: 3, // logLevel that will be used, Options are LogLevel.Error (0), LogLevel.Warn (1), LogLevel.Info (2), LogLevel.Debug (3)
     logRequestAndResponseInfo: true, // Toggle logging of the request and response bodies on and off.
     logger: myCustomLogger // (OPTIONAL) Custom logger can be passed in that implements the BaseLogger interface (e.g. debug, info, warn, error, and log functions) Otherwise console.log/error etc will be used by default.
-  }
+  },
+  customHttpAgent: new https.Agent({keepAlive: true}) // (OPTIONAL) Define a custom https agent, import https from node to use this constructor. See https://node.readthedocs.io/en/latest/api/https/#https_class_https_agent for more information. 
 };
 
 const creds = {
@@ -151,4 +152,4 @@ https://github.com/avadev/AvaTax-REST-V2-JS-SDK/blob/master/test/helpers/load_cr
 ``` bash
 # assuming a tag of v17.5.2 and a remote of 'upstream'
 git push upstream v17.5.2
-```
+```