change instructions to install fluidfoam in dev mode, setup.py is no longer used (#72)

Author: Renaud-Matthias

README.md

@@ -35,8 +35,11 @@ You can get the source code from `github
 
 The development mode is often useful. From the fluidfoam directory, run::
 
-  python -m build && pip install dist/fluidfoam*.whl --user
+  python3 -m pip install --editable . --user
+  
+Or if you are using a virtual environment, run::
 
+  python3 -m pip install --editable .
 
 Committing instructions (in development mode)
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