feat: add ability to specify config file search path

[ikatyang]

Fixes #44

[codecov-io]

Codecov Report

Merging #48 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master    #48   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           1      1           
  Lines          43     51    +8     
  Branches        6      6           
=====================================
+ Hits           43     51    +8

Impacted Files	Coverage Δ
src/prettierRule.ts	100% <100%> (ø)	⬆️

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