add python requires

[HDembinski]

No description provided.

[codecov]

Codecov Report

Merging #496 into develop will increase coverage by 0.77%.
The diff coverage is 97.10%.

@@             Coverage Diff             @@
##           develop     #496      +/-   ##
===========================================
+ Coverage    94.50%   95.28%   +0.77%     
===========================================
  Files           27       31       +4     
  Lines         2240     2968     +728     
  Branches        16        0      -16     
===========================================
+ Hits          2117     2828     +711     
- Misses         114      140      +26     
+ Partials         9        0       -9     

Impacted Files	Coverage Δ
src/iminuit/IMinuitMixin.h	100.00% <ø> (ø)
src/iminuit/PythonCaller.h	100.00% <ø> (+8.88%)	⬆️
src/iminuit/PythonFCN.h	100.00% <ø> (ø)
src/iminuit/__init__.py	66.66% <ø> (ø)
src/iminuit/_deprecated.py	100.00% <ø> (ø)
src/iminuit/color.py	100.00% <ø> (ø)
src/iminuit/info.py	0.00% <0.00%> (ø)
src/iminuit/tests/test_color.py	100.00% <ø> (ø)
src/iminuit/tests/test_describe.py	68.47% <78.94%> (+2.26%)	⬆️
src/iminuit/util.py	86.03% <86.62%> (+1.57%)	⬆️
... and 43 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update ba1bed9...d4697df. Read the comment docs.