add reading configuration from stdin

[frapposelli]

Fixes: #38

[codecov]

Codecov Report

Merging #55 (abe5a9f) into master (0e04f80) will decrease coverage by 1.27%.
The diff coverage is 45.45%.

@@            Coverage Diff             @@
##           master      #55      +/-   ##
==========================================
- Coverage   54.27%   53.00%   -1.28%     
==========================================
  Files           3        3              
  Lines         269      283      +14     
==========================================
+ Hits          146      150       +4     
- Misses        102      109       +7     
- Partials       21       24       +3     

Impacted Files	Coverage Δ
cli.go	49.60% <40.00%> (-2.29%)	⬇️
config.go	100.00% <100.00%> (+20.00%)	⬆️

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