Update changelog.md

Author: sivar2311

changelog.md

@@ -3,7 +3,7 @@
 ## Version 2.2.6
 
 New:
-- User Documentation using Doxygen
+- User Documentation using Doxygen available at https://sinricpro.github.io/esp8266-esp32-sdk
 
 Fixed: 
 - Some sendEvent functions didn't return `true`/`false`
@@ -149,4 +149,4 @@ fixed "adjustTargetTemperature" request
 **SinricProWebsocket.h**
 added server-address on websocket debug output
 
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