Fix install lbmpy without VCS

When copying lbmpy out of GIT it is not possible to install it because it can not determine its version. In fact, it is impossible to determine the version then. This MR tries to fix the situation.

setup.py

@@ -4,6 +4,7 @@ from setuptools import setup, find_packages
 import distutils
 from contextlib import redirect_stdout
 from importlib import import_module
+from warnings import warn
 
 import versioneer
 
@@ -79,6 +80,13 @@ def get_cmdclass():
 
 
 major_version = versioneer.get_version().split("+")[0]
+if major_version == "0":
+    warn("Lbmpy will be installed without VCS, thus it is impossible to determine its version. "
+         "This can lead to a faulty python requirements and thus a faulty environment")
+    pystencils_require = f'pystencils>=0.4.0'
+else:
+    pystencils_require = f'pystencils>=0.4.0,<={major_version}'
+
 setup(name='lbmpy',
       version=versioneer.get_version(),
       description='Code Generation for Lattice Boltzmann Methods',
@@ -89,7 +97,7 @@ setup(name='lbmpy',
       author_email='cs10-codegen@fau.de',
       url='https://i10git.cs.fau.de/pycodegen/lbmpy/',
       packages=['lbmpy'] + ['lbmpy.' + s for s in find_packages('lbmpy')],
-      install_requires=[f'pystencils>=0.4.0,<={major_version}', 'sympy>=1.5.1,<=1.11.1', 'numpy>=1.11.0'],
+      install_requires=[pystencils_require, 'sympy>=1.5.1,<=1.11.1', 'numpy>=1.11.0'],
       package_data={'lbmpy': ['phasefield/simplex_projection.pyx', 'phasefield/simplex_projection.c']},
       ext_modules=cython_extensions("lbmpy.phasefield.simplex_projection"),
       classifiers=[