build: add requirements.txt file

pyproject.toml

 [project]
 name = "py4foam"
 authors = [
+    { name = "Juan Pablo Carbajal", email = "juanpablo.carbajal@ost.ch" },
     { name = "Reza Housseini", email = "reza.housseini@ost.ch" },
 ]
 description = "Python utilities for OpenFOAM"
@@ -13,6 +14,7 @@ dependencies = [
     "scipy",
     "numpy",
     "fire",
+    "Pint"
 ]
 dynamic = ["readme", "version"]
 

requirements.txt

+CoolProp
+Pint
+scipy
+numpy
+fire