Readd setuptools_scm as dependency

This is needed to import the correct version.

README.md

@@ -23,6 +23,7 @@ The following packages are required in order to build the library:
     -   [Matplotlib](https://matplotlib.org/)
     -   [NumPy](https://numpy.org/)
     -   [QtPy](https://github.com/spyder-ide/qtpy)
+    -   [setuptools_scm](https://github.com/pypa/setuptools_scm/)
 -   Qt 5 or 6, with Python bindings, one of:
     - pyside2
     - pyqt5