📝 Fix typo in README

There was a misspelling in the installation instructions.

README.md

@@ -29,7 +29,7 @@ Or add it as a submodule:
 
 ```
 $ git submodule add https://github.com/linkdd/aitoolkit.git
-$ g++ -std=c++23 -Iaiotoolkit/include main.cpp -o mygame
+$ g++ -std=c++23 -Iaitoolkit/include main.cpp -o mygame
 ```
 
 > **NB:** This library is compatible with C++20.