Update README.md

Author: Ughuuu

README.md

@@ -164,7 +164,7 @@ gen/include/godot_cpp/..
 gen/include/godot_compat/..
 ```
 
-Now, all you need to do is when writting your addon/module, replace includes like these:
+Now, all you need to do is when writing your addon/module, replace includes like these:
 
 ```cpp
 #include <godot_cpp/classes/a_star_grid2d.hpp>