added some guide for reporting issue

[libliboom]

I added some comment for checking the reported issue 'cause it's so confusing to analyze it.
I think it needs how to reproduce the same issue at least.

[codecov]

Codecov Report

Merging #176 into develop will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           develop    #176   +/-   ##
=======================================
  Coverage     0.12%   0.12%           
=======================================
  Files           31      31           
  Lines         1638    1638           
  Branches       186     186           
=======================================
  Hits             2       2           
  Misses        1636    1636

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