examples : add missing code block end marker [no ci] (#17756)

This commit adds the missing code block end marker in simple-cmake-pkg
to correct the formatting.

examples/simple-cmake-pkg/README.md

@@ -18,6 +18,7 @@ cd llama.cpp
 cmake -S . -B build
 cmake --build build
 cmake --install build --prefix inst
+```
 
 ### Build simple-cmake-pkg