Add command for downloading airflow info

[feluelle]

Resolves #24

[codecov-commenter]

Codecov Report

Merging #36 (4f6278f) into master (2385793) will increase coverage by 0.14%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #36      +/-   ##
==========================================
+ Coverage   97.70%   97.84%   +0.14%     
==========================================
  Files           8        8              
  Lines         261      278      +17     
==========================================
+ Hits          255      272      +17     
  Misses          6        6              

Impacted Files	Coverage Δ
airflow_diagrams/airflow.py	97.50% <100.00%> (+0.62%)	⬆️
airflow_diagrams/cli.py	100.00% <100.00%> (ø)

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