Improved README.md

Author: vmagnin

F.png

@@ -2,20 +2,25 @@
 
 This repository contains the libcairo bindings for Fortran from the [gtk-fortran project](https://github.com/vmagnin/gtk-fortran/) available as a separate _fpm_ package.
 
-## Original project and Authors
-Origin: [gtk-fortran project](https://github.com/vmagnin/gtk-fortran/)
-Authors:
-> Vincent MAGNIN, James TAPPIN, Jens HUNGER, Jerry DE LISLE, "gtk-fortran: a GTK+ binding to build Graphical User Interfaces in Fortran", _Journal of Open Source Software,_ 4(34), 1109, 12th January 2019, [https://doi.org/10.21105/joss.01109](https://doi.org/10.21105/joss.01109)
-
-## License
-GPL-3.0-or-later
+## Testing cairo-fortran
 
-## fpm
-To use cairo-fortran within your `fpm` project, add the following to your project `fpm.toml` file:
+Each test prints nothing in the terminal but is creating a PNG file. You should therefore obtain three PNG files in the main directory of the project:
 
-```toml
-[dependencies]
-cairo-fortran = {git = "https://github.com/brocolis/cairo-fortran" }
+```bash
+$ fpm test
+cairo-auto.f90                         done.
+cairo-enums.f90                        done.
+cairo-types.f90                        done.
+libcairo-fortran.a                     done.
+test4.f90                              done.
+test1.f90                              done.
+test2.f90                              done.
+test4                                  done.
+test1                                  done.
+test2                                  done.
+[100%] Project compiled successfully.
+$ ls *.png
+axis.png  chess.png  F.png
 ```
 
 ### Example test1
@@ -24,3 +29,20 @@ cairo-fortran = {git = "https://github.com/brocolis/cairo-fortran" }
 ![test2](axis.png)
 ### Example test4
 ![test4](chess.png)
+
+## fpm
+To use cairo-fortran within your own `fpm` project, add the following to your project `fpm.toml` file:
+
+```toml
+[dependencies]
+cairo-fortran = {git = "https://github.com/vmagnin/cairo-fortran" }
+```
+
+## License
+GPL-3.0-or-later
+
+## Original project and Authors
+* Origin: [gtk-fortran project](https://github.com/vmagnin/gtk-fortran/)
+* Authors:
+> Vincent MAGNIN, James TAPPIN, Jens HUNGER, Jerry DE LISLE, "gtk-fortran: a GTK+ binding to build Graphical User Interfaces in Fortran", _Journal of Open Source Software,_ 4(34), 1109, 12th January 2019, [https://doi.org/10.21105/joss.01109](https://doi.org/10.21105/joss.01109)
+