add recursive parameter to git clone command to make sure graphlib source can be built

README.md

@@ -11,7 +11,7 @@ yay -S mathgl blas fltk
 ```
 ## Usage
 ```sh
-git clone https://voss.sarvern.no/zalox/cpp-skeleton-graphlib-fltk <project-name>
+git clone --recursive https://voss.sarvern.no/zalox/cpp-skeleton-graphlib-fltk <project-name>
 # with juci you can stop after this step and open the folder <project-name> is
 # saved and press Ctrl+Enter
 cd <project-name>