Fix CMake example, main should be treated as component

CMakeLists.txt

@@ -2,7 +2,5 @@
 # CMakeLists in this exact order for cmake to work correctly
 cmake_minimum_required(VERSION 3.5)
 
-set(MAIN_SRCS main/main.c)
-
 include($ENV{IDF_PATH}/tools/cmake/project.cmake)
 project(app-template)

main/CMakeLists.txt

@@ -0,0 +1,8 @@
+# Edit following two lines to set component requirements (see docs)
+set(COMPONENT_REQUIRES )
+set(COMPONENT_PRIV_REQUIRES )
+
+set(COMPONENT_SRCS "main.c")
+set(COMPONENT_ADD_INCLUDEDIRS "")
+
+register_component()