Adding submodule reference to Kotlin solutions repo

@see careercup#133

Author: asaph

.gitmodules

@@ -43,3 +43,6 @@
 [submodule "Ruby"]
 	path = Ruby
 	url = https://github.com/careercup/CtCI-6th-Edition-Ruby.git
+[submodule "Kotlin"]
+	path = Kotlin
+	url = https://github.com/careercup/CtCI-6th-Edition-Kotlin.git

Kotlin

@@ -43,6 +43,7 @@ Pull requests pertaining to Java solutions should be submitted to the main [CtCI
 - [CtCI-6th-Edition-JavaScript](https://github.com/careercup/CtCI-6th-Edition-JavaScript)
 - [CtCI-6th-Edition-JavaScript-ES2015](https://github.com/careercup/CtCI-6th-Edition-JavaScript-ES2015)
 - [CtCI-6th-Edition-Julia](https://github.com/careercup/CtCI-6th-Edition-Julia)
+- [CtCI-6th-Edition-Kotlin](https://github.com/careercup/CtCI-6th-Edition-Kotlin)
 - [CtCI-6th-Edition-Objective-C](https://github.com/careercup/CtCI-6th-Edition-Objective-C)
 - [CtCI-6th-Edition-php](https://github.com/careercup/CtCI-6th-Edition-php)
 - [CtCI-6th-Edition-Python](https://github.com/careercup/CtCI-6th-Edition-Python)