Added Sergey's videos

docs/en/en.json

@@ -137,6 +137,10 @@
                         "path": "https://jcash.github.io/",
                         "name": "JCash demos"
                     },
+                    {
+                        "path": "https://www.youtube.com/channel/UCjkECP_YgfCXd6Y3j3rkY_g",
+                        "name": "Sergey Lerg's video tutorials"
+                    },
                     {
                         "path": "https://www.tactxstudios.com/",
                         "name": "Tactx Studios"