Add py.typed to the package

[rytilahti]

This is necessary to inform mypy & co that the package has usable type hints

[codecov-commenter]

Codecov Report

Merging #1184 (6e54237) into master (9b099b5) will increase coverage by 0.02%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #1184      +/-   ##
==========================================
+ Coverage   78.28%   78.31%   +0.02%     
==========================================
  Files          84       84              
  Lines        9520     9532      +12     
  Branches      776      778       +2     
==========================================
+ Hits         7453     7465      +12     
  Misses       1880     1880              
  Partials      187      187              

Impacted Files	Coverage Δ
miio/integrations/yeelight/__init__.py	87.78% <0.00%> (-0.17%)	⬇️
miio/integrations/yeelight/spec_helper.py	100.00% <0.00%> (ø)
...ations/yeelight/tests/test_yeelight_spec_helper.py	100.00% <0.00%> (ø)
miio/airhumidifier_jsq.py	95.23% <0.00%> (+0.14%)	⬆️
miio/airhumidifier_mjjsq.py	93.47% <0.00%> (+0.21%)	⬆️

---

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 9b099b5...6e54237. Read the comment docs.