Fix some CMake documentation typos (#616)

The quick start instructions for CMake mention the "master"
git branch which has been replaced by "main" in the current
repo.

The main CMakeLists.txt documents how to integrate a
custom port. Fix a typo in the suggested CMake code.

CMakeLists.txt

@@ -217,7 +217,7 @@ elseif((FREERTOS_PORT STREQUAL "A_CUSTOM_PORT") AND (NOT TARGET freertos_kernel_
     "   target_include_directories(freertos_kernel_port\n"
     "     PUBLIC\n"
     "      .)\n"
-    "   taget_link_libraries(freertos_kernel_port\n"
+    "   target_link_libraries(freertos_kernel_port\n"
     "     PRIVATE\n"
     "       freertos_kernel)")
 endif()

README.md

@@ -19,7 +19,7 @@ Add the following into your project's main or a subdirectory's `CMakeLists.txt`:
 ```cmake
 FetchContent_Declare( freertos_kernel
   GIT_REPOSITORY https://github.com/FreeRTOS/FreeRTOS-Kernel.git
-  GIT_TAG        master #Note: Best practice to use specific git-hash or tagged version
+  GIT_TAG        main #Note: Best practice to use specific git-hash or tagged version
 )
 ```