Update PreCompiledFixture.h

[dalaocu]

Add comment of bcos auth contract link for easy checking.

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: -0.01% ⚠️

Comparison is base (39ebd37) 73.96% compared to head (d81048e) 73.95%.
Report is 3 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #3849      +/-   ##
==========================================
- Coverage   73.96%   73.95%   -0.01%     
==========================================
  Files         761      761              
  Lines       71939    71939              
==========================================
- Hits        53208    53203       -5     
- Misses      18731    18736       +5     

Flag	Coverage Δ
unittests	73.95% <ø> (-0.01%)	⬇️

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Files Changed	Coverage Δ
.../test/unittest/libprecompiled/PreCompiledFixture.h	99.16% <ø> (ø)

... and 2 files with indirect coverage changes

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