cmake: Add CMakeLists.txt file for WiFi station example

examples/wifi/getting_started/station/CMakeLists.txt

@@ -0,0 +1,8 @@
+# The following five lines of boilerplate have to be in your project's
+# CMakeLists in this exact order for cmake to work correctly
+cmake_minimum_required(VERSION 3.5)
+
+set(MAIN_SRCS main/station_example_main.c)
+
+include($ENV{IDF_PATH}/tools/cmake/project.cmake)
+project(wifi_station)