add deploy instructions

[zhaofeng-shu33]

Should use flask logger in production mode.
Since the app class is called in subprocess and main is not entered.
Here is an excellent article dealing about this.
Related with Issue #35.

[codecov]

Codecov Report

Merging #97 into master will increase coverage by 0.15%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master      #97      +/-   ##
==========================================
+ Coverage   87.96%   88.12%   +0.15%     
==========================================
  Files           6        7       +1     
  Lines         457      463       +6     
==========================================
+ Hits          402      408       +6     
  Misses         55       55              

Flag	Coverage Δ
#unittests	88.12% <60.00%> (+0.15%)	⬆️

Impacted Files	Coverage Δ
app_instance.py	100.00% <100.00%> (ø)
app.py	83.01% <44.44%> (+0.08%)	⬆️
utils.py	90.90% <50.00%> (+0.21%)	⬆️
jobs.py	82.60% <75.00%> (+0.38%)	⬆️

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