Add numpy as req in setup.cfg

This should have been added in 0.3.0, with the compiling subpackage.
It has been (and probably will be) fine as a transitive dependency from
OpenPathSampling. But there's no reason to do best practices.

Author: dwhswenson

setup.cfg

@@ -22,6 +22,7 @@ python_requires = >= 3.10
 install_requires =
     click
     tqdm
+    numpy
     openpathsampling >= 1.6
 packages = find: