adding comet_maths to requirements

Author: pdevis

requirements.txt

@@ -1,6 +1,7 @@
 # required modules
 numpy
 xarray
+comet_maths
 
 # for docs
 sphinx

setup.py

@@ -25,7 +25,7 @@ def read(filename):
     description="Measurement uncertainty handling in Python",
     long_description=read("README.md"),
     packages=find_packages(exclude=("tests",)),
-    install_requires=["numpy", "xarray"],
+    install_requires=["numpy", "xarray", "comet_maths"],
     extras_require={"dev": ["pre-commit", "tox", "sphinx", "sphinx_rtd_theme"]},
     classifiers=[
         "Development Status :: 2 - Pre-Alpha",