portable-RP2040: Fix typo in README.md (FreeRTOS#559)

Replace "import" with "include" in cmake code sample.

Author: paulbartell

portable/ThirdParty/GCC/RP2040/README.md

@@ -14,7 +14,7 @@ You can copy [FreeRTOS-Kernel-import.cmake](FreeRTOS-Kernel-import.cmake) into y
 add the following in your `CMakeLists.txt`:
 
 ```cmake
-import(FreeRTOS_Kernel_import.cmake)
+include(FreeRTOS_Kernel_import.cmake)
 ```
 
 This will locate the FreeRTOS kernel if it is a direct sub-module of your project, or if you provide the 
@@ -39,4 +39,4 @@ Some additional `config` options are defined [here](include/rp2040_config.h) whi
 
 ## Known Limitations
 
-- Tickless idle has not currently been tested, and is likely non-functional
+- Tickless idle has not currently been tested, and is likely non-functional